diff --git a/docs/development/testing-guidelines.md b/docs/development/testing-guidelines.md
new file mode 100644
index 00000000..593b4cfe
--- /dev/null
+++ b/docs/development/testing-guidelines.md
@@ -0,0 +1,357 @@
+# TinyTorch Testing Guidelines
+
+## Overview
+
+TinyTorch uses a **two-tier testing system** designed to provide immediate feedback during development while ensuring comprehensive validation for production use.
+
+## The Two-Tier Testing System
+
+### **Tier 1: Inline Testing (For Learning)**
+- **Purpose**: Immediate feedback during development
+- **Location**: Within `*_dev.py` files as `🧪 Test Your Implementation` sections
+- **Style**: Simple, visual, encouraging
+- **When**: After each major implementation step
+- **Audience**: Students learning the concepts
+
+### **Tier 2: Comprehensive Testing (For Validation)**
+- **Purpose**: Thorough validation and grading
+- **Location**: `tests/test_*.py` files using pytest
+- **Style**: Professional test suites with edge cases
+- **When**: After completing the module
+- **Audience**: Instructors and automated systems
+
+## Why This Approach Works
+
+### **Prevents Late-Stage Failures**
+Students get immediate feedback as they build, preventing the frustration of implementing an entire module only to discover fundamental errors during final testing.
+
+### **Builds Confidence**
+Each successful inline test provides positive reinforcement and confirms the student is on the right track.
+
+### **Teaches Testing Culture**
+Students learn to test incrementally, a crucial skill for professional development.
+
+### **Maintains Professional Standards**
+The comprehensive test suites ensure that the final package meets production-quality standards.
+
+## Inline Testing Guidelines
+
+### **When to Add Inline Tests**
+
+✅ **Add inline tests after:**
+- Each major class implementation
+- Each significant function or method
+- Complex algorithms or mathematical operations
+- Data loading or preprocessing steps
+- Any component that students might struggle with
+
+❌ **Don't add inline tests for:**
+- Trivial getters/setters
+- Simple utility functions
+- Already well-tested components
+
+### **Inline Test Structure**
+
+```python
+# %% [markdown]
+"""
+### 🧪 Test Your [Component] Implementation
+
+Let's test your [Component] implementation to ensure it's working correctly:
+"""
+
+# %%
+# Test [Component] implementation
+print("Testing [Component] Implementation:")
+print("=" * 40)
+
+try:
+    # Test 1: Basic functionality
+    component = Component()
+    test_input = create_test_input()
+    output = component(test_input)
+    
+    print(f"✅ Input: {test_input}")
+    print(f"✅ Output: {output}")
+    
+    # Check if implementation is correct
+    if validate_output(output):
+        print("🎉 [Component] implementation is CORRECT!")
+    else:
+        print("❌ [Component] implementation needs fixing")
+        print("   [Specific guidance on what to check]")
+    
+    # Test 2: Edge cases or properties
+    edge_case_test()
+    
+    print("✅ [Component] tests complete!")
+    
+except NotImplementedError:
+    print("⚠️  [Component] not implemented yet - complete the method above!")
+except Exception as e:
+    print(f"❌ Error in [Component]: {e}")
+    print("   Check your implementation in the [method] method")
+
+print()  # Add spacing
+```
+
+### **Best Practices for Inline Tests**
+
+#### **1. Immediate Feedback**
+```python
+# ✅ Good: Immediate, specific feedback
+if np.allclose(output.data.flatten(), expected):
+    print("🎉 ReLU implementation is CORRECT!")
+else:
+    print("❌ ReLU implementation needs fixing")
+    print("   Make sure negative values become 0, positive values stay unchanged")
+
+# ❌ Bad: Vague or delayed feedback
+assert np.allclose(output.data.flatten(), expected)  # Just crashes
+```
+
+#### **2. Visual and Intuitive**
+```python
+# ✅ Good: Visual confirmation
+print(f"✅ Input: {test_input.data.flatten()}")
+print(f"✅ Output: {output.data.flatten()}")
+print(f"✅ Expected: {expected}")
+
+# ❌ Bad: No visual feedback
+result = component(test_input)
+```
+
+#### **3. Property-Based Testing**
+```python
+# ✅ Good: Test mathematical properties
+all_positive = np.all(output.data > 0)
+sums_to_one = abs(np.sum(output.data) - 1.0) < 1e-6
+print(f"✅ All outputs positive: {all_positive}")
+print(f"✅ Sum equals 1.0: {sums_to_one}")
+
+# ❌ Bad: Only test specific values
+assert output.data[0] == 0.665  # Too specific, fragile
+```
+
+#### **4. Progressive Complexity**
+```python
+# ✅ Good: Start simple, add complexity
+# Test 1: Basic functionality
+basic_test()
+
+# Test 2: Edge cases
+edge_case_test()
+
+# Test 3: Numerical stability
+stability_test()
+
+# ❌ Bad: Jump to complex cases immediately
+complex_edge_case_test()  # Students get overwhelmed
+```
+
+#### **5. Helpful Error Messages**
+```python
+# ✅ Good: Actionable guidance
+except NotImplementedError:
+    print("⚠️  Sigmoid not implemented yet - complete the forward method above!")
+except Exception as e:
+    print(f"❌ Error in Sigmoid: {e}")
+    print("   Check your implementation in the forward method")
+    print("   Make sure: 0 < output < 1 and sigmoid(0) = 0.5")
+
+# ❌ Bad: Generic or unhelpful messages
+except Exception as e:
+    print(f"Error: {e}")  # Not helpful
+```
+
+## Comprehensive Testing Guidelines
+
+### **Test File Structure**
+
+```python
+"""
+Tests for TinyTorch [Module] module.
+
+These tests validate [description of what module does].
+Focus on [key aspects being tested].
+"""
+
+import pytest
+import numpy as np
+from tinytorch.core.[module] import [Classes]
+
+class Test[Component]:
+    """Test the [Component] class."""
+    
+    def test_[component]_basic_functionality(self):
+        """Test basic [component] behavior."""
+        # Test implementation
+    
+    def test_[component]_edge_cases(self):
+        """Test [component] with edge cases."""
+        # Edge case testing
+    
+    def test_[component]_properties(self):
+        """Test mathematical properties of [component]."""
+        # Property-based testing
+```
+
+### **Test Categories**
+
+#### **1. Correctness Tests**
+- Verify mathematical correctness
+- Test against known expected outputs
+- Validate algorithm implementations
+
+#### **2. Property Tests**
+- Test mathematical properties (e.g., symmetry, monotonicity)
+- Verify invariants (e.g., probability sums to 1)
+- Check boundary conditions
+
+#### **3. Edge Case Tests**
+- Extreme values (very large, very small)
+- Boundary conditions (zero, negative)
+- Empty inputs, single elements
+
+#### **4. Integration Tests**
+- Test components working together
+- Verify data flow through pipelines
+- Check compatibility between modules
+
+#### **5. Performance Tests**
+- Memory usage validation
+- Reasonable execution times
+- Scalability with data size
+
+## Module-Specific Guidelines
+
+### **Tensor Module**
+- **Inline tests**: After each arithmetic operation
+- **Focus**: Shape handling, broadcasting, data types
+- **Visual feedback**: Print shapes and values
+
+### **Activations Module**
+- **Inline tests**: After each activation function
+- **Focus**: Mathematical properties, numerical stability
+- **Visual feedback**: Input/output ranges, function properties
+
+### **Layers Module**
+- **Inline tests**: After matrix multiplication, after Dense layer
+- **Focus**: Weight initialization, forward pass correctness
+- **Visual feedback**: Weight shapes, output dimensions
+
+### **Networks Module**
+- **Inline tests**: After Sequential class, after each network type
+- **Focus**: Layer composition, architecture correctness
+- **Visual feedback**: Network structure, data flow
+
+### **DataLoader Module**
+- **Inline tests**: After Dataset, DataLoader, Normalizer
+- **Focus**: Data integrity, batching correctness, preprocessing
+- **Visual feedback**: Sample images, batch shapes, statistics
+
+## Implementation Checklist
+
+### **For Each Module**
+
+- [ ] **Inline tests after major components**
+  - [ ] Basic functionality test
+  - [ ] Property validation test
+  - [ ] Edge case test
+  - [ ] Visual feedback
+  - [ ] Helpful error messages
+
+- [ ] **Comprehensive test suite**
+  - [ ] Correctness tests
+  - [ ] Property tests
+  - [ ] Edge case tests
+  - [ ] Integration tests
+  - [ ] Performance tests
+
+- [ ] **Documentation**
+  - [ ] Clear test descriptions
+  - [ ] Expected behavior documented
+  - [ ] Error message guidance
+  - [ ] Examples of usage
+
+### **Quality Checks**
+
+- [ ] **Inline tests provide immediate feedback**
+- [ ] **Error messages are actionable**
+- [ ] **Tests cover the most likely failure modes**
+- [ ] **Visual feedback helps build intuition**
+- [ ] **Progressive complexity from simple to advanced**
+
+## Examples from Existing Modules
+
+### **Excellent Inline Testing: Activations Module**
+
+```python
+# Test ReLU implementation
+print("Testing ReLU Implementation:")
+print("=" * 40)
+
+try:
+    relu = ReLU()
+    
+    # Test 1: Basic functionality
+    test_input = Tensor([[-3, -1, 0, 1, 3]])
+    output = relu(test_input)
+    expected = [0, 0, 0, 1, 3]
+    
+    print(f"✅ Input: {test_input.data.flatten()}")
+    print(f"✅ Output: {output.data.flatten()}")
+    print(f"✅ Expected: {expected}")
+    
+    # Check if implementation is correct
+    if np.allclose(output.data.flatten(), expected):
+        print("🎉 ReLU implementation is CORRECT!")
+    else:
+        print("❌ ReLU implementation needs fixing")
+        print("   Make sure negative values become 0, positive values stay unchanged")
+    
+    print("✅ ReLU tests complete!")
+    
+except NotImplementedError:
+    print("⚠️  ReLU not implemented yet - complete the forward method above!")
+except Exception as e:
+    print(f"❌ Error in ReLU: {e}")
+    print("   Check your implementation in the forward method")
+```
+
+### **Good Progressive Testing: Tensor Module**
+
+```python
+# Test basic tensor creation
+print("Testing Tensor creation...")
+
+try:
+    # Test scalar
+    t1 = Tensor(5)
+    print(f"✅ Scalar: {t1} (shape: {t1.shape}, size: {t1.size})")
+    
+    # Test vector
+    t2 = Tensor([1, 2, 3, 4])
+    print(f"✅ Vector: {t2} (shape: {t2.shape}, size: {t2.size})")
+    
+    # Test matrix
+    t3 = Tensor([[1, 2], [3, 4]])
+    print(f"✅ Matrix: {t3} (shape: {t3.shape}, size: {t3.size})")
+    
+    print("\n🎉 All basic tests passed! Your Tensor class is working!")
+    
+except Exception as e:
+    print(f"❌ Error: {e}")
+    print("Make sure to implement all the required methods!")
+```
+
+## Conclusion
+
+The two-tier testing system ensures that students receive immediate, helpful feedback during development while maintaining professional-quality validation standards. This approach:
+
+1. **Reduces frustration** by catching errors early
+2. **Builds confidence** through positive reinforcement
+3. **Teaches good practices** for incremental testing
+4. **Maintains quality** through comprehensive validation
+
+By following these guidelines, every TinyTorch module provides an excellent learning experience while producing production-ready code. 
\ No newline at end of file
diff --git a/modules/activations/activations_dev.py b/modules/activations/activations_dev.py
index 149edb78..1654fcb2 100644
--- a/modules/activations/activations_dev.py
+++ b/modules/activations/activations_dev.py
@@ -179,6 +179,53 @@ class ReLU:
         """Allow calling the activation like a function: relu(x)"""
         return self.forward(x)
 
+# %% [markdown]
+"""
+### 🧪 Test Your ReLU Implementation
+
+Let's test your ReLU implementation right away to make sure it's working correctly:
+"""
+
+# %%
+# Test ReLU implementation
+print("Testing ReLU Implementation:")
+print("=" * 40)
+
+try:
+    relu = ReLU()
+    
+    # Test 1: Basic functionality
+    test_input = Tensor([[-3, -1, 0, 1, 3]])
+    output = relu(test_input)
+    expected = [0, 0, 0, 1, 3]
+    
+    print(f"✅ Input: {test_input.data.flatten()}")
+    print(f"✅ Output: {output.data.flatten()}")
+    print(f"✅ Expected: {expected}")
+    
+    # Check if implementation is correct
+    if np.allclose(output.data.flatten(), expected):
+        print("🎉 ReLU implementation is CORRECT!")
+    else:
+        print("❌ ReLU implementation needs fixing")
+        print("   Make sure negative values become 0, positive values stay unchanged")
+    
+    # Test 2: Edge cases
+    edge_cases = Tensor([[0.0, -0.0, 1e-10, -1e-10]])
+    edge_output = relu(edge_cases)
+    print(f"✅ Edge cases: {edge_cases.data.flatten()}")
+    print(f"✅ Edge output: {edge_output.data.flatten()}")
+    
+    print("✅ ReLU tests complete!")
+    
+except NotImplementedError:
+    print("⚠️  ReLU not implemented yet - complete the forward method above!")
+except Exception as e:
+    print(f"❌ Error in ReLU: {e}")
+    print("   Check your implementation in the forward method")
+
+print()  # Add spacing
+
 # %% [markdown]
 """
 ## Step 3: Sigmoid Activation Function
@@ -247,6 +294,63 @@ class Sigmoid:
         """Allow calling the activation like a function: sigmoid(x)"""
         return self.forward(x)
 
+# %% [markdown]
+"""
+### 🧪 Test Your Sigmoid Implementation
+
+Let's test your Sigmoid implementation to ensure it's working correctly:
+"""
+
+# %%
+# Test Sigmoid implementation
+print("Testing Sigmoid Implementation:")
+print("=" * 40)
+
+try:
+    sigmoid = Sigmoid()
+    
+    # Test 1: Basic functionality
+    test_input = Tensor([[-2, -1, 0, 1, 2]])
+    output = sigmoid(test_input)
+    
+    print(f"✅ Input: {test_input.data.flatten()}")
+    print(f"✅ Output: {output.data.flatten()}")
+    
+    # Check properties
+    all_positive = np.all(output.data > 0)
+    all_less_than_one = np.all(output.data < 1)
+    zero_maps_to_half = abs(sigmoid(Tensor([0])).data[0] - 0.5) < 1e-6
+    
+    print(f"✅ All outputs positive: {all_positive}")
+    print(f"✅ All outputs < 1: {all_less_than_one}")
+    print(f"✅ Sigmoid(0) ≈ 0.5: {zero_maps_to_half}")
+    
+    if all_positive and all_less_than_one and zero_maps_to_half:
+        print("🎉 Sigmoid implementation is CORRECT!")
+    else:
+        print("❌ Sigmoid implementation needs fixing")
+        print("   Make sure: 0 < output < 1 and sigmoid(0) = 0.5")
+    
+    # Test 2: Numerical stability
+    extreme_values = Tensor([[-1000, 1000]])
+    extreme_output = sigmoid(extreme_values)
+    print(f"✅ Extreme values: {extreme_values.data.flatten()}")
+    print(f"✅ Extreme output: {extreme_output.data.flatten()}")
+    
+    # Should not have NaN or inf
+    no_nan_inf = not (np.isnan(extreme_output.data).any() or np.isinf(extreme_output.data).any())
+    print(f"✅ No NaN/Inf: {no_nan_inf}")
+    
+    print("✅ Sigmoid tests complete!")
+    
+except NotImplementedError:
+    print("⚠️  Sigmoid not implemented yet - complete the forward method above!")
+except Exception as e:
+    print(f"❌ Error in Sigmoid: {e}")
+    print("   Check your implementation in the forward method")
+
+print()  # Add spacing
+
 # %% [markdown]
 """
 ## Step 4: Tanh Activation Function
@@ -315,6 +419,65 @@ class Tanh:
         """Allow calling the activation like a function: tanh(x)"""
         return self.forward(x)
 
+# %% [markdown]
+"""
+### 🧪 Test Your Tanh Implementation
+
+Let's test your Tanh implementation to ensure it's working correctly:
+"""
+
+# %%
+# Test Tanh implementation
+print("Testing Tanh Implementation:")
+print("=" * 40)
+
+try:
+    tanh = Tanh()
+    
+    # Test 1: Basic functionality
+    test_input = Tensor([[-2, -1, 0, 1, 2]])
+    output = tanh(test_input)
+    
+    print(f"✅ Input: {test_input.data.flatten()}")
+    print(f"✅ Output: {output.data.flatten()}")
+    
+    # Check properties
+    in_range = np.all(np.abs(output.data) < 1)
+    zero_maps_to_zero = abs(tanh(Tensor([0])).data[0]) < 1e-6
+    symmetric = np.allclose(tanh(Tensor([1])).data, -tanh(Tensor([-1])).data)
+    
+    print(f"✅ All outputs in (-1, 1): {in_range}")
+    print(f"✅ Tanh(0) ≈ 0: {zero_maps_to_zero}")
+    print(f"✅ Symmetric (tanh(-x) = -tanh(x)): {symmetric}")
+    
+    if in_range and zero_maps_to_zero and symmetric:
+        print("🎉 Tanh implementation is CORRECT!")
+    else:
+        print("❌ Tanh implementation needs fixing")
+        print("   Make sure: -1 < output < 1, tanh(0) = 0, and tanh(-x) = -tanh(x)")
+    
+    # Test 2: Compare with expected values
+    expected_values = {
+        0: 0.0,
+        1: 0.7616,  # approximately
+        -1: -0.7616,  # approximately
+    }
+    
+    for input_val, expected in expected_values.items():
+        actual = tanh(Tensor([input_val])).data[0]
+        close = abs(actual - expected) < 0.001
+        print(f"✅ Tanh({input_val}) ≈ {expected}: {close} (got {actual:.4f})")
+    
+    print("✅ Tanh tests complete!")
+    
+except NotImplementedError:
+    print("⚠️  Tanh not implemented yet - complete the forward method above!")
+except Exception as e:
+    print(f"❌ Error in Tanh: {e}")
+    print("   Check your implementation in the forward method")
+
+print()  # Add spacing
+
 # %% [markdown]
 """
 ## Step 5: Softmax Activation Function
@@ -385,6 +548,74 @@ class Softmax:
         """Allow calling the activation like a function: softmax(x)"""
         return self.forward(x)
 
+# %% [markdown]
+"""
+### 🧪 Test Your Softmax Implementation
+
+Let's test your Softmax implementation to ensure it's working correctly:
+"""
+
+# %%
+# Test Softmax implementation
+print("Testing Softmax Implementation:")
+print("=" * 40)
+
+try:
+    softmax = Softmax()
+    
+    # Test 1: Basic functionality
+    test_input = Tensor([[2, 1, 0]])
+    output = softmax(test_input)
+    
+    print(f"✅ Input: {test_input.data.flatten()}")
+    print(f"✅ Output: {output.data.flatten()}")
+    
+    # Check properties
+    all_positive = np.all(output.data > 0)
+    sums_to_one = abs(np.sum(output.data) - 1.0) < 1e-6
+    largest_input_largest_output = np.argmax(test_input.data) == np.argmax(output.data)
+    
+    print(f"✅ All outputs positive: {all_positive}")
+    print(f"✅ Sum equals 1.0: {sums_to_one} (sum = {np.sum(output.data):.6f})")
+    print(f"✅ Largest input → largest output: {largest_input_largest_output}")
+    
+    if all_positive and sums_to_one and largest_input_largest_output:
+        print("🎉 Softmax implementation is CORRECT!")
+    else:
+        print("❌ Softmax implementation needs fixing")
+        print("   Make sure: all outputs > 0, sum = 1.0, and largest input gets largest probability")
+    
+    # Test 2: Numerical stability
+    extreme_input = Tensor([[1000, 999, 998]])
+    extreme_output = softmax(extreme_input)
+    print(f"✅ Extreme input: {extreme_input.data.flatten()}")
+    print(f"✅ Extreme output: {extreme_output.data.flatten()}")
+    
+    # Should not have NaN or inf
+    no_nan_inf = not (np.isnan(extreme_output.data).any() or np.isinf(extreme_output.data).any())
+    extreme_sums_to_one = abs(np.sum(extreme_output.data) - 1.0) < 1e-6
+    
+    print(f"✅ No NaN/Inf: {no_nan_inf}")
+    print(f"✅ Extreme case sums to 1: {extreme_sums_to_one}")
+    
+    # Test 3: Equal inputs should give equal probabilities
+    equal_input = Tensor([[1, 1, 1]])
+    equal_output = softmax(equal_input)
+    expected_prob = 1.0 / 3.0
+    all_equal = np.allclose(equal_output.data, expected_prob)
+    print(f"✅ Equal inputs → equal probabilities: {all_equal}")
+    print(f"   Expected: {expected_prob:.3f}, Got: {equal_output.data.flatten()}")
+    
+    print("✅ Softmax tests complete!")
+    
+except NotImplementedError:
+    print("⚠️  Softmax not implemented yet - complete the forward method above!")
+except Exception as e:
+    print(f"❌ Error in Softmax: {e}")
+    print("   Check your implementation in the forward method")
+
+print()  # Add spacing
+
 # %% [markdown]
 """
 ## Testing Our Activation Functions