diff --git a/internal/core/repositories/repositories.go b/internal/core/repositories/repositories.go
new file mode 100644
index 0000000..fe0b38c
--- /dev/null
+++ b/internal/core/repositories/repositories.go
@@ -0,0 +1,23 @@
+package repositories
+
+import (
+	"CodeSCE/internal/core/models"
+	"context"
+)
+
+type AssessmentRepository interface {
+	Create(ctx context.Context, assessment *models.AssessmentTemplate) error
+	List(ctx context.Context) ([]models.AssessmentTemplate, error)
+	GetByID(ctx context.Context, id int64) (*models.AssessmentTemplate, error)
+}
+
+type QuestionRepository interface {
+	Create(ctx context.Context, question *models.Question) error
+	GetByID(ctx context.Context, id int64) (*models.Question, error)
+	ListByAssessmentID(ctx context.Context, assessmentID int64) ([]models.Question, error)
+}
+
+type TestCaseRepository interface {
+	CreateMany(ctx context.Context, questionID int64, testCases []models.TestCase) error
+	ListByQuestionID(ctx context.Context, questionID int64) ([]models.TestCase, error)
+}
diff --git a/internal/core/services/assessment_service.go b/internal/core/services/assessment_service.go
new file mode 100644
index 0000000..117ef90
--- /dev/null
+++ b/internal/core/services/assessment_service.go
@@ -0,0 +1,193 @@
+package services
+
+import (
+	"CodeSCE/internal/core/models"
+	"CodeSCE/internal/core/repositories"
+	"context"
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrAssessmentNotFound = errors.New("assessment not found")
+	ErrQuestionNotFound   = errors.New("question not found")
+	ErrWrongAssessment    = errors.New("question does not belong to this assessment")
+)
+
+type FieldError struct {
+	Field   string
+	Message string
+}
+
+func (e FieldError) Error() string {
+	return e.Field + ": " + e.Message
+}
+
+type QuestionWithTestCases struct {
+	models.Question
+	TestCases []models.TestCase `json:"testCases,omitempty"`
+}
+
+type AssessmentWithQuestions struct {
+	models.AssessmentTemplate
+	Questions []QuestionWithTestCases `json:"questions"`
+}
+
+type AssessmentService struct {
+	assessmentRepo repositories.AssessmentRepository
+	questionRepo   repositories.QuestionRepository
+	testCaseRepo   repositories.TestCaseRepository
+}
+
+func NewAssessmentService(
+	ar repositories.AssessmentRepository,
+	qr repositories.QuestionRepository,
+	tr repositories.TestCaseRepository,
+) *AssessmentService {
+	return &AssessmentService{
+		assessmentRepo: ar,
+		questionRepo:   qr,
+		testCaseRepo:   tr,
+	}
+}
+
+func (s *AssessmentService) CreateAssessment(ctx context.Context, assessment *models.AssessmentTemplate) error {
+	if assessment == nil {
+		return FieldError{Field: "assessment", Message: "required"}
+	}
+	if err := validateAssessment(assessment); err != nil {
+		return err
+	}
+	return s.assessmentRepo.Create(ctx, assessment)
+}
+
+func (s *AssessmentService) ListAssessments(ctx context.Context) ([]models.AssessmentTemplate, error) {
+	return s.assessmentRepo.List(ctx)
+}
+
+func (s *AssessmentService) GetAssessment(ctx context.Context, id int64) (*AssessmentWithQuestions, error) {
+	a, err := s.assessmentRepo.GetByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	if a == nil {
+		return nil, ErrAssessmentNotFound
+	}
+	questions, err := s.questionRepo.ListByAssessmentID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]QuestionWithTestCases, len(questions))
+	for i := range questions {
+		result[i].Question = questions[i]
+		if questions[i].Type == "code" {
+			tcs, err := s.testCaseRepo.ListByQuestionID(ctx, questions[i].ID)
+			if err != nil {
+				return nil, err
+			}
+			result[i].TestCases = tcs
+		}
+	}
+	return &AssessmentWithQuestions{AssessmentTemplate: *a, Questions: result}, nil
+}
+
+func (s *AssessmentService) AddQuestion(ctx context.Context, assessmentID int64, question *models.Question) error {
+	if question == nil {
+		return FieldError{Field: "question", Message: "required"}
+	}
+	question.AssessmentTemplateID = assessmentID
+	if err := validateQuestion(question); err != nil {
+		return err
+	}
+	a, err := s.assessmentRepo.GetByID(ctx, assessmentID)
+	if err != nil {
+		return err
+	}
+	if a == nil {
+		return ErrAssessmentNotFound
+	}
+	return s.questionRepo.Create(ctx, question)
+}
+
+// AddTestCases persists test cases for a question. assessmentID must match the question's assessment (route :id) so ownership can be enforced.
+func (s *AssessmentService) AddTestCases(ctx context.Context, assessmentID, questionID int64, testCases []models.TestCase) error {
+	if err := validateTestCases(testCases); err != nil {
+		return err
+	}
+	q, err := s.questionRepo.GetByID(ctx, questionID)
+	if err != nil {
+		return err
+	}
+	if q == nil {
+		return ErrQuestionNotFound
+	}
+	if q.AssessmentTemplateID != assessmentID {
+		return ErrWrongAssessment
+	}
+	return s.testCaseRepo.CreateMany(ctx, questionID, testCases)
+}
+
+func validateAssessment(a *models.AssessmentTemplate) error {
+	if a.Title == "" {
+		return FieldError{Field: "title", Message: "required"}
+	}
+	if a.DurationMinutes <= 0 {
+		return FieldError{Field: "duration_minutes", Message: "must be greater than 0"}
+	}
+	return nil
+}
+
+func validateQuestion(q *models.Question) error {
+	if q.Prompt == "" {
+		return FieldError{Field: "prompt", Message: "required"}
+	}
+	if err := validateQuestionType(q.Type); err != nil {
+		return err
+	}
+	if err := validatePositiveScore(q.Score, "score"); err != nil {
+		return err
+	}
+	if q.Type == "code" {
+		if q.Language == nil || *q.Language == "" {
+			return FieldError{Field: "language", Message: "required for code questions"}
+		}
+	}
+	if questionTypeRequiresOptions(q.Type) && q.Options == nil {
+		return FieldError{Field: "options", Message: "required for MCQ questions"}
+	}
+	return nil
+}
+
+func validateQuestionType(typ string) error {
+	switch typ {
+	case "mcq", "multi_select", "short_answer", "code":
+		return nil
+	default:
+		return FieldError{Field: "type", Message: "must be mcq, multi_select, short_answer, or code"}
+	}
+}
+
+func questionTypeRequiresOptions(typ string) bool {
+	switch typ {
+	case "mcq", "multi_select":
+		return true
+	default:
+		return false
+	}
+}
+
+func validateTestCases(cases []models.TestCase) error {
+	for i := range cases {
+		if err := validatePositiveScore(cases[i].Score, fmt.Sprintf("test_cases[%d].score", i)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validatePositiveScore(score int, field string) error {
+	if score <= 0 {
+		return FieldError{Field: field, Message: "must be greater than 0"}
+	}
+	return nil
+}