diff --git a/client/src/components/regularStudentScheduleModal/RegularStudentScheduleModal.tsx b/client/src/components/regularStudentScheduleModal/RegularStudentScheduleModal.tsx
index 2fe4fabd..02309084 100644
--- a/client/src/components/regularStudentScheduleModal/RegularStudentScheduleModal.tsx
+++ b/client/src/components/regularStudentScheduleModal/RegularStudentScheduleModal.tsx
@@ -120,9 +120,9 @@ const ModalContent = ({
 
   return (
     <div className="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50 p-4">
-      <div className="bg-[#2A2433] rounded-2xl p-10 w-full max-w-5xl max-h-[85vh] flex flex-col">
-        <div className="flex items-center justify-between mb-10">
-          <h2 className="text-3xl font-bold text-white">
+      <div className="bg-[#2A2433] rounded-2xl p-4 sm:p-6 lg:p-10 w-full max-w-5xl max-h-[85vh] flex flex-col">
+        <div className="flex items-center justify-between mb-6 lg:mb-10">
+          <h2 className="text-xl sm:text-2xl lg:text-3xl font-bold text-white">
             Weekly Schedule for {studentName}
           </h2>
           <button
@@ -135,22 +135,22 @@ const ModalContent = ({
 
         <div className="flex-1 overflow-y-auto pr-2">
           {savedSlots.length > 0 && (
-            <div className="mb-8">
-              <h3 className="text-white text-lg font-semibold mb-4">
+            <div className="mb-6 lg:mb-8">
+              <h3 className="text-white text-base sm:text-lg font-semibold mb-3 lg:mb-4">
                 Scheduled Lessons ({savedSlots.length})
               </h3>
-              <div className="space-y-3">
+              <div className="space-y-2 lg:space-y-3">
                 {savedSlots.map((slot, index) => (
                   <div
                     key={index}
-                    className="bg-[#1E1D28] rounded-lg px-6 py-4 flex items-center justify-between"
+                    className="bg-[#1E1D28] rounded-lg px-4 sm:px-6 py-3 sm:py-4 flex items-center justify-between"
                   >
-                    <span className="text-white text-base">
+                    <span className="text-white text-sm sm:text-base">
                       {slot.day}, {slot.hour}:00
                     </span>
                     <button
                       onClick={() => handleRemoveSlot(index)}
-                      className="text-red-400 hover:text-red-300 text-sm font-medium px-3 py-1 rounded hover:bg-red-400/10 transition-colors"
+                      className="text-red-400 hover:text-red-300 text-xs sm:text-sm font-medium px-2 sm:px-3 py-1 rounded hover:bg-red-400/10 transition-colors"
                     >
                       Remove
                     </button>
@@ -160,13 +160,15 @@ const ModalContent = ({
             </div>
           )}
 
-          <div className="space-y-6">
-            <h3 className="text-white text-xl font-semibold">Add Lesson</h3>
+          <div className="space-y-4 lg:space-y-6">
+            <h3 className="text-white text-lg sm:text-xl font-semibold">
+              Add Lesson
+            </h3>
 
-            <div className="bg-[#1E1D28] rounded-xl p-10">
-              <div className="grid grid-cols-2 gap-10 mb-8">
+            <div className="bg-[#1E1D28] rounded-xl p-4 sm:p-6 lg:p-10">
+              <div className="grid grid-cols-1 lg:grid-cols-2 gap-4 sm:gap-6 lg:gap-10 mb-6 lg:mb-8">
                 <div>
-                  <label className="block text-gray-300 text-lg font-medium mb-5">
+                  <label className="block text-gray-300 text-sm sm:text-base lg:text-lg font-medium mb-3 lg:mb-5">
                     Day
                   </label>
                   <SelectComponent
@@ -178,7 +180,7 @@ const ModalContent = ({
                 </div>
 
                 <div>
-                  <label className="block text-gray-300 text-lg font-medium mb-5">
+                  <label className="block text-gray-300 text-sm sm:text-base lg:text-lg font-medium mb-3 lg:mb-5">
                     Time
                   </label>
                   <SelectComponent
@@ -191,16 +193,16 @@ const ModalContent = ({
               </div>
 
               {isDuplicate && (
-                <div className="mb-4 px-4 py-3 bg-red-500/20 border border-red-500/50 rounded-lg">
-                  <p className="text-red-300 text-sm">
+                <div className="mb-4 px-3 sm:px-4 py-2 sm:py-3 bg-red-500/20 border border-red-500/50 rounded-lg">
+                  <p className="text-red-300 text-xs sm:text-sm">
                     This time slot is already added to the schedule
                   </p>
                 </div>
               )}
 
               {isOccupied && !isDuplicate && (
-                <div className="mb-4 px-4 py-3 bg-red-500/20 border border-red-500/50 rounded-lg">
-                  <p className="text-red-300 text-sm">
+                <div className="mb-4 px-3 sm:px-4 py-2 sm:py-3 bg-red-500/20 border border-red-500/50 rounded-lg">
+                  <p className="text-red-300 text-xs sm:text-sm">
                     This time slot is already occupied by another Regular
                     Student
                   </p>
@@ -210,7 +212,7 @@ const ModalContent = ({
               <Button
                 onClick={handleAddLesson}
                 variant="secondary"
-                className="w-full text-base py-4"
+                className="w-full text-sm sm:text-base py-3 sm:py-4"
                 disabled={cannotAdd}
               >
                 {isDuplicate
@@ -223,18 +225,18 @@ const ModalContent = ({
           </div>
         </div>
 
-        <div className="mt-6 pt-6 border-t border-gray-700 flex justify-end gap-5">
+        <div className="mt-4 sm:mt-6 pt-4 sm:pt-6 border-t border-gray-700 flex flex-col lg:flex-row justify-end gap-3 sm:gap-5">
           <Button
             onClick={handleCancel}
             variant="secondary"
-            className="px-10 py-3 text-base"
+            className="px-6 sm:px-10 py-2 sm:py-3 text-sm sm:text-base order-2 lg:order-1"
           >
             Cancel
           </Button>
           <Button
             onClick={handleSave}
             variant="primary"
-            className="px-10 py-3 text-base"
+            className="px-6 sm:px-10 py-2 sm:py-3 text-sm sm:text-base order-1 lg:order-2"
           >
             Save Schedule
           </Button>
diff --git a/client/src/components/regularStudentScheduleModal/ViewScheduleModal.tsx b/client/src/components/regularStudentScheduleModal/ViewScheduleModal.tsx
index 4e6ece91..059177bf 100644
--- a/client/src/components/regularStudentScheduleModal/ViewScheduleModal.tsx
+++ b/client/src/components/regularStudentScheduleModal/ViewScheduleModal.tsx
@@ -19,9 +19,9 @@ export const ViewScheduleModal = ({
 
   return (
     <div className="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50 p-4">
-      <div className="bg-[#2A2433] rounded-2xl p-10 w-full max-w-4xl max-h-[85vh] flex flex-col">
-        <div className="flex items-center justify-between mb-10">
-          <h2 className="text-3xl font-bold text-white">
+      <div className="bg-[#2A2433] rounded-2xl p-4 sm:p-6 lg:p-10 w-full max-w-4xl max-h-[85vh] flex flex-col">
+        <div className="flex items-center justify-between mb-6 lg:mb-10">
+          <h2 className="text-xl sm:text-2xl lg:text-3xl font-bold text-white">
             Weekly Schedule with {teacherName}
           </h2>
           <button
@@ -34,28 +34,30 @@ export const ViewScheduleModal = ({
 
         <div className="flex-1 overflow-y-auto pr-2">
           {schedule.length === 0 ? (
-            <div className="text-center py-12">
-              <p className="text-gray-400 text-lg">No schedule set yet</p>
+            <div className="text-center py-8 lg:py-12">
+              <p className="text-gray-400 text-base lg:text-lg">
+                No schedule set yet
+              </p>
               <p className="text-gray-500 text-sm mt-2">
                 Your teacher hasn&apos;t set up a weekly schedule yet
               </p>
             </div>
           ) : (
             <div>
-              <h3 className="text-white text-lg font-semibold mb-6">
+              <h3 className="text-white text-base sm:text-lg font-semibold mb-4 lg:mb-6">
                 Your Lessons ({schedule.length} per week)
               </h3>
-              <div className="space-y-4">
+              <div className="space-y-3 lg:space-y-4">
                 {schedule.map((slot, index) => (
                   <div
                     key={index}
-                    className="bg-[#1E1D28] rounded-lg px-8 py-5 flex items-center"
+                    className="bg-[#1E1D28] rounded-lg px-4 sm:px-6 lg:px-8 py-3 sm:py-4 lg:py-5 flex items-center"
                   >
                     <div className="flex-1">
-                      <span className="text-white text-lg font-medium">
+                      <span className="text-white text-base sm:text-lg font-medium">
                         {slot.day}
                       </span>
-                      <span className="text-gray-400 text-lg ml-4">
+                      <span className="text-gray-400 text-base sm:text-lg ml-2 sm:ml-4">
                         at {slot.hour}:00
                       </span>
                     </div>
@@ -66,11 +68,11 @@ export const ViewScheduleModal = ({
           )}
         </div>
 
-        <div className="mt-8 pt-6 border-t border-gray-700 flex justify-center">
+        <div className="mt-6 lg:mt-8 pt-4 lg:pt-6 border-t border-gray-700 flex justify-center">
           <Button
             onClick={onClose}
             variant="primary"
-            className="px-12 py-3 text-base"
+            className="px-8 sm:px-12 py-2 sm:py-3 text-sm sm:text-base"
           >
             Close
           </Button>
diff --git a/client/src/components/teacherProfileSection/LessonSchedule.tsx b/client/src/components/teacherProfileSection/LessonSchedule.tsx
index 9b27012f..058f20c6 100644
--- a/client/src/components/teacherProfileSection/LessonSchedule.tsx
+++ b/client/src/components/teacherProfileSection/LessonSchedule.tsx
@@ -82,10 +82,12 @@ const ModalContent = ({
   };
 
   return (
-    <div className="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50 p-4">
-      <div className="bg-[#2A2433] rounded-2xl p-8 w-full max-w-[95vw] max-h-[95vh] overflow-y-auto">
-        <div className="flex items-center justify-between mb-6">
-          <h2 className="text-3xl font-bold text-white">Lesson schedule</h2>
+    <div className="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50 p-2 sm:p-4">
+      <div className="bg-[#2A2433] rounded-2xl p-4 sm:p-6 lg:p-8 w-full max-w-[95vw] max-h-[95vh] overflow-y-auto">
+        <div className="flex items-center justify-between mb-4 sm:mb-6">
+          <h2 className="text-xl sm:text-2xl lg:text-3xl font-bold text-white">
+            Lesson schedule
+          </h2>
           <button
             onClick={onClose}
             className="text-white hover:text-purple-400 transition-colors"
@@ -99,11 +101,11 @@ const ModalContent = ({
             <table className="w-full border-collapse">
               <thead>
                 <tr>
-                  <th className="border border-gray-600 p-2 sticky left-0 bg-[#2A2433] z-10"></th>
+                  <th className="border border-gray-600 p-1 sm:p-2 sticky left-0 bg-[#2A2433] z-10"></th>
                   {HOURS.map((hour) => (
                     <th
                       key={hour}
-                      className="border border-gray-600 p-2 text-white text-sm min-w-[60px]"
+                      className="border border-gray-600 p-1 sm:p-2 text-white text-xs sm:text-sm min-w-[50px] sm:min-w-[60px]"
                     >
                       {formatHour(hour)}
                     </th>
@@ -113,8 +115,9 @@ const ModalContent = ({
               <tbody>
                 {DAYS.map((day) => (
                   <tr key={day}>
-                    <td className="border border-gray-600 p-3 text-white font-medium sticky left-0 bg-[#2A2433] z-10 min-w-[100px]">
-                      {day}
+                    <td className="border border-gray-600 p-2 sm:p-3 text-white font-medium sticky left-0 bg-[#2A2433] z-10 min-w-[80px] sm:min-w-[100px] text-xs sm:text-sm">
+                      <span className="hidden sm:inline">{day}</span>
+                      <span className="sm:hidden">{day.slice(0, 3)}</span>
                     </td>
                     {HOURS.map((hour) => {
                       const key = `${day}-${hour}`;
@@ -125,7 +128,7 @@ const ModalContent = ({
                         <td
                           key={hour}
                           onClick={() => !isBlocked && toggleSlot(day, hour)}
-                          className={`border border-gray-600 p-1 transition-colors min-w-[60px] min-h-[50px] ${
+                          className={`border border-gray-600 p-1 transition-colors min-w-[50px] sm:min-w-[60px] min-h-[40px] sm:min-h-[50px] ${
                             isBlocked
                               ? "bg-red-900 cursor-not-allowed"
                               : isSelected
@@ -142,21 +145,29 @@ const ModalContent = ({
           </div>
         </div>
 
-        <div className="mt-6 flex items-center gap-4">
+        <div className="mt-4 sm:mt-6 flex flex-col sm:flex-row items-start sm:items-center gap-2 sm:gap-4">
           <div className="flex items-center gap-2">
-            <div className="w-6 h-6 bg-purple-500 rounded"></div>
-            <span className="text-white text-sm">Available time</span>
+            <div className="w-4 h-4 sm:w-6 sm:h-6 bg-purple-500 rounded"></div>
+            <span className="text-white text-xs sm:text-sm">
+              Available time
+            </span>
           </div>
           {bookedSlots.length > 0 && (
             <div className="flex items-center gap-2">
-              <div className="w-6 h-6 bg-red-900 rounded"></div>
-              <span className="text-white text-sm">Regular Students</span>
+              <div className="w-4 h-4 sm:w-6 sm:h-6 bg-red-900 rounded"></div>
+              <span className="text-white text-xs sm:text-sm">
+                Regular Students
+              </span>
             </div>
           )}
         </div>
 
-        <div className="mt-6 flex justify-center">
-          <Button onClick={handleSave} variant="primary" className="px-12">
+        <div className="mt-4 sm:mt-6 flex justify-center">
+          <Button
+            onClick={handleSave}
+            variant="primary"
+            className="px-8 sm:px-12 py-2 sm:py-3 text-sm sm:text-base"
+          >
             Save
           </Button>
         </div>
diff --git a/client/src/components/ui/pagination/Pagination.tsx b/client/src/components/ui/pagination/Pagination.tsx
index c27ef2f2..b01210dd 100644
--- a/client/src/components/ui/pagination/Pagination.tsx
+++ b/client/src/components/ui/pagination/Pagination.tsx
@@ -94,7 +94,7 @@ export const Pagination = ({
   }
 
   return (
-    <div className="flex items-center justify-center gap-4">
+    <div className="flex items-center justify-center gap-4 mb-4">
       <Button
         variant="link"
         className={paginationButtonStyles({ theme, shape, state: "inactive" })}
diff --git a/server/src/services/appointment/appointment.service.ts b/server/src/services/appointment/appointment.service.ts
index e792d4a3..5be1b441 100644
--- a/server/src/services/appointment/appointment.service.ts
+++ b/server/src/services/appointment/appointment.service.ts
@@ -8,11 +8,10 @@ import {
 } from "../../types/appointment/appointment.types.js";
 import { AppointmentCommand } from "../../repositories/commandRepositories/appointment.command.js";
 import { AppointmentQuery } from "../../repositories/queryRepositories/appointment.query.js";
-import { StudentModel } from "../../db/schemes/studentSchema.js";
-import { TeacherModel } from "../../db/schemes/teacherSchema.js";
 import { ConversationCommand } from "../../repositories/commandRepositories/conversation.command.js";
 import { logError, logWarning } from "../../utils/logging.js";
 import { VideoCallModel } from "../../db/schemes/videoCallSchema.js";
+import { AppointmentBusinessValidation } from "../../validation/appointment/appointmentBusinessValidation.js";
 
 @injectable()
 export class AppointmentService {
@@ -26,41 +25,7 @@ export class AppointmentService {
   ) {}
 
   async createAppointment(data: CreateAppointmentType) {
-    const student = await StudentModel.findOne({ id: data.studentId });
-    if (!student) {
-      throw new Error("Student not found");
-    }
-
-    const teacher = await TeacherModel.findOne({ id: data.teacherId });
-    if (!teacher) {
-      throw new Error("Teacher not found");
-    }
-
-    if (data.teacherId === data.studentId) {
-      throw new Error("Teachers cannot book appointments with themselves");
-    }
-
-    const appointmentDate = new Date(data.date);
-    const today = new Date();
-    today.setHours(0, 0, 0, 0);
-    appointmentDate.setHours(0, 0, 0, 0);
-
-    if (appointmentDate < today) {
-      throw new Error("Cannot create appointments in the past");
-    }
-
-    if (appointmentDate.getTime() === today.getTime()) {
-      const [hours, minutes] = data.time.split(":").map(Number);
-      const appointmentDateTime = new Date(data.date);
-      appointmentDateTime.setHours(hours, minutes, 0, 0);
-
-      const now = new Date();
-      if (appointmentDateTime < now) {
-        throw new Error(
-          "Cannot create appointments for times that have already passed",
-        );
-      }
-    }
+    await AppointmentBusinessValidation.validateCreateAppointment(data);
 
     const appointment = {
       id: randomUUID(),
@@ -187,13 +152,11 @@ export class AppointmentService {
   async deleteAppointment(id: string, userId: string) {
     const appointment = await this.appointmentQuery.getAppointmentById(id);
 
-    if (!appointment) {
-      throw new Error("Appointment not found");
-    }
-
-    if (appointment.teacherId !== userId && appointment.studentId !== userId) {
-      throw new Error("Unauthorized to delete this appointment");
-    }
+    AppointmentBusinessValidation.validateAppointmentExists(appointment);
+    AppointmentBusinessValidation.validateDeleteAuthorization(
+      appointment,
+      userId,
+    );
 
     const updateData = {
       status: "rejected" as const,
@@ -339,13 +302,11 @@ export class AppointmentService {
   async setRegularStudent(id: string, teacherId: string) {
     const appointment = await this.appointmentQuery.getAppointmentById(id);
 
-    if (!appointment) {
-      throw new Error("Appointment not found");
-    }
-
-    if (appointment.teacherId !== teacherId) {
-      throw new Error("Unauthorized to modify this appointment");
-    }
+    AppointmentBusinessValidation.validateAppointmentExists(appointment);
+    AppointmentBusinessValidation.validateTeacherAuthorization(
+      appointment,
+      teacherId,
+    );
 
     const updated = await this.appointmentCommand.setRegularStudent(id);
     return updated ? this.formatAppointmentResponse(updated) : null;
@@ -354,13 +315,11 @@ export class AppointmentService {
   async removeRegularStudent(id: string, teacherId: string) {
     const appointment = await this.appointmentQuery.getAppointmentById(id);
 
-    if (!appointment) {
-      throw new Error("Appointment not found");
-    }
-
-    if (appointment.teacherId !== teacherId) {
-      throw new Error("Unauthorized to modify this appointment");
-    }
+    AppointmentBusinessValidation.validateAppointmentExists(appointment);
+    AppointmentBusinessValidation.validateTeacherAuthorization(
+      appointment,
+      teacherId,
+    );
 
     const updated = await this.appointmentCommand.removeRegularStudent(id);
     return updated ? this.formatAppointmentResponse(updated) : null;
@@ -373,17 +332,13 @@ export class AppointmentService {
   ) {
     const appointment = await this.appointmentQuery.getAppointmentById(id);
 
-    if (!appointment) {
-      throw new Error("Appointment not found");
-    }
-
-    if (appointment.teacherId !== teacherId) {
-      throw new Error("Unauthorized to modify this appointment");
-    }
-
-    if (!appointment.isRegularStudent) {
-      throw new Error("Cannot set weekly schedule for a non-regular student");
-    }
+    AppointmentBusinessValidation.validateAppointmentExists(appointment);
+    AppointmentBusinessValidation.validateTeacherAuthorization(
+      appointment,
+      teacherId,
+    );
+    AppointmentBusinessValidation.validateRegularStudent(appointment);
+    AppointmentBusinessValidation.validateWeeklyScheduleData(weeklySchedule);
 
     const updated = await this.appointmentCommand.updateWeeklySchedule(
       id,
diff --git a/server/src/validation/appointment/appointmentBusinessValidation.ts b/server/src/validation/appointment/appointmentBusinessValidation.ts
new file mode 100644
index 00000000..a92b8bd6
--- /dev/null
+++ b/server/src/validation/appointment/appointmentBusinessValidation.ts
@@ -0,0 +1,132 @@
+import { StudentModel } from "../../db/schemes/studentSchema.js";
+import { TeacherModel } from "../../db/schemes/teacherSchema.js";
+import { CreateAppointmentType } from "../../types/appointment/appointment.types.js";
+import { AppointmentScheduleValidation } from "./appointmentScheduleValidation.js";
+import { APPOINTMENT_VALIDATION_CONSTANTS } from "./appointmentValidation.constants.js";
+
+export class AppointmentBusinessValidation {
+  static async validateStudentExists(studentId: string) {
+    const student = await StudentModel.findOne({ id: studentId });
+    if (!student) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.STUDENT_NOT_FOUND,
+      );
+    }
+    return student;
+  }
+
+  static async validateTeacherExists(teacherId: string) {
+    const teacher = await TeacherModel.findOne({ id: teacherId });
+    if (!teacher) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.TEACHER_NOT_FOUND,
+      );
+    }
+    return teacher;
+  }
+
+  static validateNotSelfBooking(teacherId: string, studentId: string) {
+    if (teacherId === studentId) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.SELF_BOOKING,
+      );
+    }
+  }
+
+  static validateAppointmentDate(date: string) {
+    const appointmentDate = new Date(date);
+    const today = new Date();
+    today.setHours(0, 0, 0, 0);
+    appointmentDate.setHours(0, 0, 0, 0);
+
+    if (appointmentDate < today) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.PAST_DATE,
+      );
+    }
+
+    return appointmentDate;
+  }
+
+  static validateAppointmentTime(date: string, time: string) {
+    AppointmentScheduleValidation.validateWorkingHours(time);
+
+    const appointmentDate = new Date(date);
+    const today = new Date();
+    today.setHours(0, 0, 0, 0);
+    appointmentDate.setHours(0, 0, 0, 0);
+
+    if (appointmentDate.getTime() === today.getTime()) {
+      const [hours, minutes] = time.split(":").map(Number);
+      const appointmentDateTime = new Date(date);
+      appointmentDateTime.setHours(hours, minutes, 0, 0);
+
+      const now = new Date();
+      if (appointmentDateTime < now) {
+        throw new Error(
+          APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.PAST_TIME,
+        );
+      }
+    }
+
+    AppointmentScheduleValidation.validateMinimumAdvanceTime(date, time);
+    AppointmentScheduleValidation.validateMaximumAdvanceTime(date);
+  }
+
+  static async validateCreateAppointment(data: CreateAppointmentType) {
+    await Promise.all([
+      this.validateStudentExists(data.studentId),
+      this.validateTeacherExists(data.teacherId),
+    ]);
+
+    this.validateNotSelfBooking(data.teacherId, data.studentId);
+    this.validateAppointmentDate(data.date);
+    this.validateAppointmentTime(data.date, data.time);
+  }
+
+  static validateDeleteAuthorization(
+    appointment: { teacherId: string; studentId: string },
+    userId: string,
+  ) {
+    if (appointment.teacherId !== userId && appointment.studentId !== userId) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.UNAUTHORIZED_DELETE,
+      );
+    }
+  }
+
+  static validateTeacherAuthorization(
+    appointment: { teacherId: string },
+    teacherId: string,
+  ) {
+    if (appointment.teacherId !== teacherId) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.UNAUTHORIZED_MODIFY,
+      );
+    }
+  }
+
+  static validateRegularStudent(appointment: { isRegularStudent?: boolean }) {
+    if (!appointment.isRegularStudent) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.NOT_REGULAR_STUDENT,
+      );
+    }
+  }
+
+  static validateAppointmentExists(
+    appointment: unknown,
+  ): asserts appointment is NonNullable<typeof appointment> {
+    if (!appointment) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.APPOINTMENT_NOT_FOUND,
+      );
+    }
+  }
+
+  static validateWeeklyScheduleData(
+    weeklySchedule: { day: string; hour: number }[],
+  ) {
+    AppointmentScheduleValidation.validateWeeklySchedule(weeklySchedule);
+  }
+}
diff --git a/server/src/validation/appointment/appointmentScheduleValidation.ts b/server/src/validation/appointment/appointmentScheduleValidation.ts
new file mode 100644
index 00000000..a042a07c
--- /dev/null
+++ b/server/src/validation/appointment/appointmentScheduleValidation.ts
@@ -0,0 +1,157 @@
+import { APPOINTMENT_VALIDATION_CONSTANTS } from "./appointmentValidation.constants.js";
+
+export class AppointmentScheduleValidation {
+  static validateTimeFormat(time: string): boolean {
+    return APPOINTMENT_VALIDATION_CONSTANTS.TIME_FORMAT_REGEX.test(time);
+  }
+
+  static validateWorkingHours(time: string): boolean {
+    if (!this.validateTimeFormat(time)) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.INVALID_TIME_FORMAT,
+      );
+    }
+
+    const [hours] = time.split(":").map(Number);
+    const { WORKING_HOURS_START, WORKING_HOURS_END } =
+      APPOINTMENT_VALIDATION_CONSTANTS;
+
+    if (hours < WORKING_HOURS_START || hours >= WORKING_HOURS_END) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.INVALID_WORKING_HOURS(
+          WORKING_HOURS_START,
+          WORKING_HOURS_END,
+        ),
+      );
+    }
+
+    return true;
+  }
+
+  static validateWeekDay(day: string): boolean {
+    const { VALID_WEEK_DAYS } = APPOINTMENT_VALIDATION_CONSTANTS;
+
+    if (
+      !VALID_WEEK_DAYS.includes(
+        day.toLowerCase() as (typeof VALID_WEEK_DAYS)[number],
+      )
+    ) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.INVALID_DAY(
+          day,
+          VALID_WEEK_DAYS,
+        ),
+      );
+    }
+
+    return true;
+  }
+
+  static validateScheduleHour(hour: number): boolean {
+    if (!Number.isInteger(hour) || hour < 0 || hour > 23) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.INVALID_HOUR,
+      );
+    }
+
+    const { WORKING_HOURS_START, WORKING_HOURS_END } =
+      APPOINTMENT_VALIDATION_CONSTANTS;
+
+    if (hour < WORKING_HOURS_START || hour >= WORKING_HOURS_END) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.INVALID_SCHEDULE_HOUR(
+          WORKING_HOURS_START,
+          WORKING_HOURS_END,
+        ),
+      );
+    }
+
+    return true;
+  }
+
+  static validateWeeklySchedule(
+    weeklySchedule: { day: string; hour: number }[],
+  ): boolean {
+    if (!Array.isArray(weeklySchedule)) {
+      throw new Error("Weekly schedule must be an array");
+    }
+
+    if (weeklySchedule.length === 0) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.EMPTY_WEEKLY_SCHEDULE,
+      );
+    }
+
+    if (
+      weeklySchedule.length >
+      APPOINTMENT_VALIDATION_CONSTANTS.MAX_WEEKLY_SCHEDULE_ENTRIES
+    ) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES
+          .TOO_MANY_SCHEDULE_ENTRIES,
+      );
+    }
+
+    const uniqueDays = new Set();
+
+    for (const schedule of weeklySchedule) {
+      if (
+        !schedule.day ||
+        typeof schedule.day !== "string" ||
+        typeof schedule.hour !== "number"
+      ) {
+        throw new Error(
+          APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES
+            .INVALID_SCHEDULE_ENTRY,
+        );
+      }
+
+      this.validateWeekDay(schedule.day);
+      this.validateScheduleHour(schedule.hour);
+
+      const dayLower = schedule.day.toLowerCase();
+      if (uniqueDays.has(dayLower)) {
+        throw new Error(
+          APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.DUPLICATE_DAY(
+            schedule.day,
+          ),
+        );
+      }
+      uniqueDays.add(dayLower);
+    }
+
+    return true;
+  }
+
+  static validateMinimumAdvanceTime(date: string, time: string): boolean {
+    const appointmentDateTime = new Date(`${date}T${time}:00`);
+    const now = new Date();
+
+    if (
+      appointmentDateTime.getTime() - now.getTime() <
+      APPOINTMENT_VALIDATION_CONSTANTS.MINIMUM_ADVANCE_TIME_MS
+    ) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.MINIMUM_ADVANCE_TIME,
+      );
+    }
+
+    return true;
+  }
+
+  static validateMaximumAdvanceTime(date: string): boolean {
+    const appointmentDate = new Date(date);
+    const now = new Date();
+
+    if (
+      appointmentDate.getTime() - now.getTime() >
+      APPOINTMENT_VALIDATION_CONSTANTS.MAXIMUM_ADVANCE_TIME_MS
+    ) {
+      throw new Error(
+        APPOINTMENT_VALIDATION_CONSTANTS.ERROR_MESSAGES.MAXIMUM_ADVANCE_TIME,
+      );
+    }
+
+    return true;
+  }
+}
diff --git a/server/src/validation/appointment/appointmentValidation.constants.ts b/server/src/validation/appointment/appointmentValidation.constants.ts
new file mode 100644
index 00000000..340677bc
--- /dev/null
+++ b/server/src/validation/appointment/appointmentValidation.constants.ts
@@ -0,0 +1,51 @@
+export const APPOINTMENT_VALIDATION_CONSTANTS = {
+  WORKING_HOURS_START: 8,
+  WORKING_HOURS_END: 22,
+
+  MINIMUM_ADVANCE_TIME_MS: 60 * 60 * 1000,
+  MAXIMUM_ADVANCE_TIME_MS: 90 * 24 * 60 * 60 * 1000,
+
+  MAX_WEEKLY_SCHEDULE_ENTRIES: 7,
+
+  VALID_WEEK_DAYS: [
+    "monday",
+    "tuesday",
+    "wednesday",
+    "thursday",
+    "friday",
+    "saturday",
+    "sunday",
+  ] as const,
+
+  TIME_FORMAT_REGEX: /^([0-1]?[0-9]|2[0-3]):[0-5][0-9]$/,
+
+  ERROR_MESSAGES: {
+    STUDENT_NOT_FOUND: "Student not found",
+    TEACHER_NOT_FOUND: "Teacher not found",
+    SELF_BOOKING: "Teachers cannot book appointments with themselves",
+    PAST_DATE: "Cannot create appointments in the past",
+    PAST_TIME: "Cannot create appointments for times that have already passed",
+    APPOINTMENT_NOT_FOUND: "Appointment not found",
+    UNAUTHORIZED_DELETE: "Unauthorized to delete this appointment",
+    UNAUTHORIZED_MODIFY: "Unauthorized to modify this appointment",
+    NOT_REGULAR_STUDENT: "Cannot set weekly schedule for a non-regular student",
+    INVALID_TIME_FORMAT: "Invalid time format. Use HH:MM format",
+    INVALID_WORKING_HOURS: (start: number, end: number) =>
+      `Appointments can only be scheduled between ${start}:00 and ${end}:00`,
+    INVALID_DAY: (day: string, validDays: readonly string[]) =>
+      `Invalid day: ${day}. Valid days are: ${validDays.join(", ")}`,
+    INVALID_HOUR: "Hour must be an integer between 0 and 23",
+    INVALID_SCHEDULE_HOUR: (start: number, end: number) =>
+      `Schedule hour must be between ${start} and ${end - 1}`,
+    MINIMUM_ADVANCE_TIME:
+      "Appointments must be scheduled at least 1 hour in advance",
+    MAXIMUM_ADVANCE_TIME:
+      "Appointments cannot be scheduled more than 3 months in advance",
+    EMPTY_WEEKLY_SCHEDULE: "Weekly schedule cannot be empty",
+    TOO_MANY_SCHEDULE_ENTRIES:
+      "Weekly schedule cannot have more than 7 entries",
+    DUPLICATE_DAY: (day: string) => `Duplicate day in schedule: ${day}`,
+    INVALID_SCHEDULE_ENTRY:
+      "Each schedule entry must have a valid day and hour",
+  },
+} as const;