diff --git a/requirements.txt b/requirements.txt
index 5d9efb5..f2821b2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,5 @@
 fastapi
 uvicorn
 httpx
-watchfiles
\ No newline at end of file
+watchfiles
+pytest
\ No newline at end of file
diff --git a/src/app.py b/src/app.py
index 4ebb1d9..81efb31 100644
--- a/src/app.py
+++ b/src/app.py
@@ -38,6 +38,42 @@
         "schedule": "Mondays, Wednesdays, Fridays, 2:00 PM - 3:00 PM",
         "max_participants": 30,
         "participants": ["john@mergington.edu", "olivia@mergington.edu"]
+    },
+    "Basketball Team": {
+        "description": "Competitive basketball practice and games",
+        "schedule": "Mondays and Wednesdays, 4:00 PM - 5:30 PM",
+        "max_participants": 15,
+        "participants": ["james@mergington.edu"]
+    },
+    "Tennis Club": {
+        "description": "Tennis instruction and match play",
+        "schedule": "Tuesdays and Thursdays, 4:00 PM - 5:00 PM",
+        "max_participants": 16,
+        "participants": ["sarah@mergington.edu", "alex@mergington.edu"]
+    },
+    "Drama Club": {
+        "description": "Perform in plays and musicals",
+        "schedule": "Wednesdays and Fridays, 3:30 PM - 5:00 PM",
+        "max_participants": 25,
+        "participants": ["grace@mergington.edu"]
+    },
+    "Art Studio": {
+        "description": "Painting, drawing, and sculpture techniques",
+        "schedule": "Mondays and Thursdays, 3:30 PM - 4:45 PM",
+        "max_participants": 18,
+        "participants": ["isabella@mergington.edu", "lucas@mergington.edu"]
+    },
+    "Debate Team": {
+        "description": "Develop argumentation and public speaking skills",
+        "schedule": "Tuesdays, 4:00 PM - 5:30 PM",
+        "max_participants": 10,
+        "participants": ["benjamin@mergington.edu"]
+    },
+    "Science Club": {
+        "description": "Explore experiments and scientific discovery",
+        "schedule": "Fridays, 3:30 PM - 4:45 PM",
+        "max_participants": 20,
+        "participants": ["nina@mergington.edu", "ryan@mergington.edu"]
     }
 }
 
@@ -62,6 +98,33 @@ def signup_for_activity(activity_name: str, email: str):
     # Get the specific activity
     activity = activities[activity_name]
 
+    # Check if student is already signed up
+    if email in activity["participants"]:
+        raise HTTPException(status_code=400, detail="Student already signed up for this activity")
+
+    # Check if activity is full
+    if len(activity["participants"]) >= activity["max_participants"]:
+        raise HTTPException(status_code=400, detail="Activity is full")
+
     # Add student
     activity["participants"].append(email)
     return {"message": f"Signed up {email} for {activity_name}"}
+
+
+@app.delete("/activities/{activity_name}/participants/{email}")
+def remove_participant(activity_name: str, email: str):
+    """Remove a participant from an activity"""
+    # Validate activity exists
+    if activity_name not in activities:
+        raise HTTPException(status_code=404, detail="Activity not found")
+    
+    activity = activities[activity_name]
+    
+    # Check if participant exists
+    if email not in activity["participants"]:
+        raise HTTPException(status_code=404, detail="Participant not found")
+    
+    # Remove participant
+    activity["participants"].remove(email)
+    return {"message": f"Removed {email} from {activity_name}"}
+
diff --git a/src/static/app.js b/src/static/app.js
index dcc1e38..16f2ca8 100644
--- a/src/static/app.js
+++ b/src/static/app.js
@@ -25,6 +25,19 @@ document.addEventListener("DOMContentLoaded", () => {
           <p>${details.description}</p>
           <p><strong>Schedule:</strong> ${details.schedule}</p>
           <p><strong>Availability:</strong> ${spotsLeft} spots left</p>
+          <div class="participants-section">
+            <strong>Participants (${details.participants.length}):</strong>
+            <ul>
+              ${details.participants.length > 0 
+                ? details.participants.map(email => `
+                    <li class="participant-item">
+                      <span>${email}</span>
+                      <button class="delete-participant-btn" data-activity="${name}" data-email="${email}" title="Remove participant">✕</button>
+                    </li>
+                  `).join('') 
+                : '<li class="no-participants">No participants yet</li>'}
+            </ul>
+          </div>
         `;
 
         activitiesList.appendChild(activityCard);
@@ -62,6 +75,7 @@ document.addEventListener("DOMContentLoaded", () => {
         messageDiv.textContent = result.message;
         messageDiv.className = "success";
         signupForm.reset();
+        fetchActivities();
       } else {
         messageDiv.textContent = result.detail || "An error occurred";
         messageDiv.className = "error";
@@ -81,6 +95,47 @@ document.addEventListener("DOMContentLoaded", () => {
     }
   });
 
+  // Handle delete participant button clicks
+  document.addEventListener("click", async (event) => {
+    if (event.target.classList.contains("delete-participant-btn")) {
+      const activity = event.target.dataset.activity;
+      const email = event.target.dataset.email;
+
+      if (!confirm(`Remove ${email} from ${activity}?`)) {
+        return;
+      }
+
+      try {
+        const response = await fetch(
+          `/activities/${encodeURIComponent(activity)}/participants/${encodeURIComponent(email)}`,
+          { method: "DELETE" }
+        );
+
+        if (response.ok) {
+          // Refresh activities list
+          fetchActivities();
+          messageDiv.textContent = `Removed ${email} from ${activity}`;
+          messageDiv.className = "success";
+          messageDiv.classList.remove("hidden");
+
+          setTimeout(() => {
+            messageDiv.classList.add("hidden");
+          }, 5000);
+        } else {
+          const result = await response.json();
+          messageDiv.textContent = result.detail || "Failed to remove participant";
+          messageDiv.className = "error";
+          messageDiv.classList.remove("hidden");
+        }
+      } catch (error) {
+        messageDiv.textContent = "Error removing participant";
+        messageDiv.className = "error";
+        messageDiv.classList.remove("hidden");
+        console.error("Error removing participant:", error);
+      }
+    }
+  });
+
   // Initialize app
   fetchActivities();
 });
diff --git a/src/static/styles.css b/src/static/styles.css
index a533b32..5af7943 100644
--- a/src/static/styles.css
+++ b/src/static/styles.css
@@ -74,6 +74,64 @@ section h3 {
   margin-bottom: 8px;
 }
 
+.participants-section {
+  margin-top: 15px;
+  padding-top: 15px;
+  border-top: 2px solid #e0e0e0;
+}
+
+.participants-section strong {
+  display: block;
+  margin-bottom: 8px;
+  color: #1a237e;
+  font-size: 14px;
+}
+
+.participants-section ul {
+  list-style: none;
+  margin-left: 0;
+  padding-left: 0;
+}
+
+.participant-item {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  font-size: 14px;
+  color: #555;
+  margin-bottom: 6px;
+  padding: 8px;
+  background-color: #f0f0f0;
+  border-radius: 3px;
+}
+
+.participant-item span {
+  word-break: break-word;
+  flex: 1;
+}
+
+.delete-participant-btn {
+  background-color: #d32f2f;
+  color: white;
+  border: none;
+  padding: 4px 8px;
+  font-size: 14px;
+  border-radius: 3px;
+  cursor: pointer;
+  transition: background-color 0.2s;
+  margin-left: 10px;
+  flex-shrink: 0;
+}
+
+.delete-participant-btn:hover {
+  background-color: #b71c1c;
+}
+
+.participants-section li.no-participants {
+  color: #999;
+  font-style: italic;
+}
+
 .form-group {
   margin-bottom: 15px;
 }
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_activities.py b/tests/test_activities.py
new file mode 100644
index 0000000..0b7be28
--- /dev/null
+++ b/tests/test_activities.py
@@ -0,0 +1,176 @@
+"""
+Tests for Mergington High School extracurricular activities API
+Using AAA (Arrange-Act-Assert) pattern
+"""
+
+from fastapi.testclient import TestClient
+from src.app import app
+
+client = TestClient(app)
+
+
+class TestGetActivities:
+    """Test suite for GET /activities endpoint"""
+    
+    def test_get_activities_returns_all_activities(self):
+        # Arrange
+        expected_keys = {"Chess Club", "Programming Class", "Gym Class", 
+                        "Basketball Team", "Tennis Club", "Drama Club", 
+                        "Art Studio", "Debate Team", "Science Club"}
+        
+        # Act
+        response = client.get("/activities")
+        
+        # Assert
+        assert response.status_code == 200
+        activities = response.json()
+        assert set(activities.keys()) == expected_keys
+    
+    def test_get_activities_returns_correct_structure(self):
+        # Arrange
+        required_fields = {"description", "schedule", "max_participants", "participants"}
+        
+        # Act
+        response = client.get("/activities")
+        activities = response.json()
+        
+        # Assert
+        assert response.status_code == 200
+        for activity_name, activity_data in activities.items():
+            assert set(activity_data.keys()) == required_fields
+            assert isinstance(activity_data["participants"], list)
+            assert isinstance(activity_data["max_participants"], int)
+
+
+class TestSignupForActivity:
+    """Test suite for POST /activities/{activity_name}/signup endpoint"""
+    
+    def test_signup_success(self):
+        # Arrange
+        test_email = "test.student@mergington.edu"
+        activity_name = "Chess Club"
+        initial_participant_count = len(client.get("/activities").json()[activity_name]["participants"])
+        
+        # Act
+        response = client.post(
+            f"/activities/{activity_name}/signup",
+            params={"email": test_email}
+        )
+        
+        # Assert
+        assert response.status_code == 200
+        assert "Signed up" in response.json()["message"]
+        
+        # Verify participant was added
+        updated_activities = client.get("/activities").json()
+        assert test_email in updated_activities[activity_name]["participants"]
+        assert len(updated_activities[activity_name]["participants"]) == initial_participant_count + 1
+    
+    def test_signup_duplicate_participant_error(self):
+        # Arrange
+        test_email = "duplicate.test@mergington.edu"
+        activity_name = "Programming Class"
+        
+        # Sign up once (should succeed)
+        client.post(f"/activities/{activity_name}/signup", params={"email": test_email})
+        
+        # Act - Try to sign up again
+        response = client.post(
+            f"/activities/{activity_name}/signup",
+            params={"email": test_email}
+        )
+        
+        # Assert
+        assert response.status_code == 400
+        assert "already signed up" in response.json()["detail"]
+    
+    def test_signup_invalid_activity_error(self):
+        # Arrange
+        test_email = "test@mergington.edu"
+        invalid_activity = "Nonexistent Club"
+        
+        # Act
+        response = client.post(
+            f"/activities/{invalid_activity}/signup",
+            params={"email": test_email}
+        )
+        
+        # Assert
+        assert response.status_code == 404
+        assert "Activity not found" in response.json()["detail"]
+    
+    def test_signup_activity_full_error(self):
+        # Arrange
+        activity_name = "Debate Team"  # Has max_participants: 10
+        activities = client.get("/activities").json()
+        
+        # Fill up the activity
+        test_emails = [f"student{i}@mergington.edu" for i in range(10)]
+        for email in test_emails:
+            client.post(f"/activities/{activity_name}/signup", params={"email": email})
+        
+        # Act - Try to sign up when full
+        response = client.post(
+            f"/activities/{activity_name}/signup",
+            params={"email": "extra.student@mergington.edu"}
+        )
+        
+        # Assert
+        assert response.status_code == 400
+        assert "full" in response.json()["detail"]
+
+
+class TestRemoveParticipant:
+    """Test suite for DELETE /activities/{activity_name}/participants/{email} endpoint"""
+    
+    def test_remove_participant_success(self):
+        # Arrange
+        test_email = "remove.test@mergington.edu"
+        activity_name = "Tennis Club"
+        
+        # Sign up the participant
+        client.post(f"/activities/{activity_name}/signup", params={"email": test_email})
+        activities = client.get("/activities").json()
+        initial_count = len(activities[activity_name]["participants"])
+        
+        # Act
+        response = client.delete(
+            f"/activities/{activity_name}/participants/{test_email}"
+        )
+        
+        # Assert
+        assert response.status_code == 200
+        assert "Removed" in response.json()["message"]
+        
+        # Verify participant was removed
+        updated_activities = client.get("/activities").json()
+        assert test_email not in updated_activities[activity_name]["participants"]
+        assert len(updated_activities[activity_name]["participants"]) == initial_count - 1
+    
+    def test_remove_participant_not_found_error(self):
+        # Arrange
+        nonexistent_email = "notinactivity@mergington.edu"
+        activity_name = "Art Studio"
+        
+        # Act
+        response = client.delete(
+            f"/activities/{activity_name}/participants/{nonexistent_email}"
+        )
+        
+        # Assert
+        assert response.status_code == 404
+        assert "Participant not found" in response.json()["detail"]
+    
+    def test_remove_participant_activity_not_found_error(self):
+        # Arrange
+        test_email = "test@mergington.edu"
+        invalid_activity = "Fake Club"
+        
+        # Act
+        response = client.delete(
+            f"/activities/{invalid_activity}/participants/{test_email}"
+        )
+        
+        # Assert
+        assert response.status_code == 404
+        assert "Activity not found" in response.json()["detail"]