Introduction to Functions

Active learning works because functions are best understood through doing. Students need to see definitions become reusable blocks of code to grasp their power. Writing, calling, and debugging functions in pairs or groups makes abstract concepts concrete and memorable.

• Year 9
• Computing
• 4 activities
• 20 min–45 min

Learning Objectives

1. Define and call Python functions, incorporating parameters and return values.
2. Calculate the area of a rectangle by constructing a Python function that accepts length and width as parameters.
3. Explain how functions contribute to code readability and manageability by breaking down complex tasks.
4. Analyze the benefits of using functions to reduce code repetition and improve program structure.

Flipped Classroom

⏱ 30 min·Pairs

Pair Programming: Rectangle Area Function

Pairs write a function def rectangle_area(length, width): that returns length * width. They call it with user inputs and print results. Switch roles after 10 minutes to test and refine each other's code.

Prepare & details

Explain how functions contribute to making code more readable and manageable.

Facilitation Tip: During Pair Programming, have students alternate roles every 5 minutes so both contribute to writing and debugging the rectangle area function.

Setup: Standard classroom, flexible for group activities during class

Materials: Pre-class content (video/reading with guiding questions), Readiness check or entrance ticket, In-class application activity, Reflection journal

• Understand
• Apply
• Analyze
• Self-Management
• Self-Awareness

Flipped Classroom

⏱ 45 min·Small Groups

Small Groups: Function Chain Challenge

Groups create three functions: one for perimeter, one for area, one combining both for a shape report. Chain calls so the report function uses the others. Share and run on class projector.

Prepare & details

Construct a function that calculates the area of a rectangle given its length and width.

Facilitation Tip: In the Function Chain Challenge, provide starter code with missing links to force students to trace parameter flow between functions.

Setup: Standard classroom, flexible for group activities during class

Materials: Pre-class content (video/reading with guiding questions), Readiness check or entrance ticket, In-class application activity, Reflection journal

• Understand
• Apply
• Analyze
• Self-Management
• Self-Awareness

Flipped Classroom

⏱ 20 min·Whole Class

Whole Class: Code Review Relay

Project a buggy function code. Students take turns suggesting fixes for parameter errors or missing returns. Vote on best fixes and test live as a class.

Prepare & details

Analyze the benefits of using functions to avoid code repetition.

Facilitation Tip: For Code Review Relay, assign roles like ‘reader’, ‘tester’, and ‘documenter’ so every student engages with the code’s purpose and structure.

Setup: Standard classroom, flexible for group activities during class

Materials: Pre-class content (video/reading with guiding questions), Readiness check or entrance ticket, In-class application activity, Reflection journal

• Understand
• Apply
• Analyze
• Self-Management
• Self-Awareness

Flipped Classroom

⏱ 25 min·Individual

Individual: Extension Functions

Students build a personalised function, like grade calculator with score parameter, then return letter grade. Submit for peer review next lesson.

Prepare & details

Explain how functions contribute to making code more readable and manageable.

Setup: Standard classroom, flexible for group activities during class

Materials: Pre-class content (video/reading with guiding questions), Readiness check or entrance ticket, In-class application activity, Reflection journal

• Understand
• Apply
• Analyze
• Self-Management
• Self-Awareness

Teaching This Topic

Teach functions by starting with a clear problem, like calculating rectangle areas, then solving it step by step. Avoid rushing to advanced topics; mastery of simple functions builds confidence. Research shows that students grasp scope and returns better when they debug their own code, so design activities that surface errors naturally.

What to Expect

Successful learning looks like students confidently defining functions with parameters, calling them correctly, and explaining why returns matter. They should articulate how functions reduce repetition and improve code structure in their own words.

Watch Out for These Misconceptions

Common Misconception

During Pair Programming, watch for students who assume the function runs as soon as it is defined.

What to Teach Instead

Have partners add a print statement after the function definition to confirm it only executes when called, using area(5, 3) to demonstrate the sequence.

Common Misconception

During Function Chain Challenge, listen for students who think parameters alter values outside the function.

What to Teach Instead

Ask groups to swap variables before and after calling functions, then compare values to show parameters create local copies.

Common Misconception

During Code Review Relay, observe students treating return values as print statements.

What to Teach Instead

Require students to assign the return to a variable and print that variable separately, so they see returns and prints serve different purposes.

Assessment Ideas

Exit Ticket

After Pair Programming, give students a code snippet with a rectangle area function. Ask them to identify the definition, write the call area(4, 6), and state the output while explaining how the return value is used.

Quick Check

After Function Chain Challenge, ask students to define a temperature conversion function during a quick write. Check that they correctly define parameters and returns, then call it with 25 to produce 77.

Discussion Prompt

During Code Review Relay, pose the question: ‘How would you organize a website with functions for user profiles and login handling?’ Have students write one example function each and share with the group.

Extensions & Scaffolding

• Challenge: Ask students to write a function that calculates the area of a triangle using the rectangle function as a helper.
• Scaffolding: Provide a partially completed function with comments guiding parameter placement and return statements.
• Deeper exploration: Introduce default parameters by having students modify the rectangle function to calculate area when only one side is provided.

Key Vocabulary

function	A named block of code that performs a specific task and can be reused multiple times within a program.
parameter	A variable listed inside the parentheses in a function definition, acting as a placeholder for input values the function will receive.
argument	The actual value that is passed into a function when it is called, corresponding to a parameter.
return value	The value that a function sends back to the part of the program that called it, often the result of a calculation or operation.
call	To execute or run a function by using its name followed by parentheses, optionally providing arguments.