Defining and Calling Functions

Teaching functions through active learning turns abstract concepts into concrete experiences. Students see firsthand how reusing code saves effort and reduces errors, which builds confidence and long-term retention. Hands-on practice also lets them test their own assumptions, turning confusion into clarity through immediate feedback.

• Grade 10
• Computer Science
• 4 activities
• 25 min–45 min

Learning Objectives

1. Construct a Python function that accepts two integer arguments and returns their sum.
2. Analyze a given code snippet to identify instances of code redundancy that could be refactored into functions.
3. Explain the difference between a global variable and a local variable within the context of a Python program.
4. Compare the execution flow of a program with and without the use of functions for a specific task.
5. Design a simple program that utilizes at least three distinct functions to achieve a defined output.

Peer Teaching

⏱ 35 min·Pairs

Pair Programming: Shape Calculator Functions

Pairs write three functions: one for circle area, one for rectangle area, and one to compare results. They call each with user inputs and refactor a script with repeated calculations. Pairs swap code to test and suggest improvements.

Prepare & details

Analyze how functions reduce code redundancy and improve modularity.

Facilitation Tip: During Pair Programming, circulate and ask each pair to explain why they chose a particular parameter name, reinforcing the connection between function design and real-world use.

Setup: Presentation area at front, or multiple teaching stations

Materials: Topic assignment cards, Lesson planning template, Peer feedback form, Visual aid supplies

• Understand
• Apply
• Analyze
• Create
• Self-Management
• Relationship Skills

Peer Teaching

⏱ 40 min·Small Groups

Small Groups: Scope Debugging Challenge

Groups receive buggy code with scope errors, like modifying global variables inside functions. They predict outcomes, run the code, trace variable changes, and rewrite with proper local variables. Discuss fixes as a group before sharing one solution with the class.

Prepare & details

Construct a function to perform a specific task with given inputs.

Facilitation Tip: In the Scope Debugging Challenge, provide code with intentional scope errors and ask groups to trace variable lifetimes using highlighters or annotations on printed listings.

Setup: Presentation area at front, or multiple teaching stations

Materials: Topic assignment cards, Lesson planning template, Peer feedback form, Visual aid supplies

• Understand
• Apply
• Analyze
• Create
• Self-Management
• Relationship Skills

Peer Teaching

⏱ 45 min·Whole Class

Whole Class: Function Design Relay

Divide class into teams. Each team starts a function for a task like string manipulation, passes it to the next team to add parameters and calls, then iterates until complete. Class votes on the most modular final function.

Prepare & details

Explain the concept of scope for variables defined within and outside functions.

Facilitation Tip: For the Function Design Relay, prepare a set of starter function signatures on cards so students can physically arrange and test their sequence of calls.

Setup: Presentation area at front, or multiple teaching stations

Materials: Topic assignment cards, Lesson planning template, Peer feedback form, Visual aid supplies

• Understand
• Apply
• Analyze
• Create
• Self-Management
• Relationship Skills

Peer Teaching

⏱ 25 min·Individual

Individual: Personal Code Refactor

Students select their own prior program with redundancy, identify repeatable logic, define functions to replace it, and document before-and-after differences. They run tests to verify functionality and submit reflections on improvements.

Prepare & details

Analyze how functions reduce code redundancy and improve modularity.

Facilitation Tip: In Personal Code Refactor, remind students to leave comments in their original messy code so they can compare it to their clean version during reflection.

Setup: Presentation area at front, or multiple teaching stations

Materials: Topic assignment cards, Lesson planning template, Peer feedback form, Visual aid supplies

• Understand
• Apply
• Analyze
• Create
• Self-Management
• Relationship Skills

Teaching This Topic

Teachers find success when they treat functions as tools, not just syntax. Begin with physical metaphors, like passing labeled objects to a teammate who performs a task and returns a result. Avoid overloading students with too many rules at once. Instead, let them discover patterns through repeated use, and correct misconceptions as they arise during active work.

What to Expect

By the end of these activities, students will define functions with parameters, call them with arguments, and track variable scope. They will explain why functions improve program structure and identify when to use returns versus prints. Successful learning shows in clean, reusable code and clear explanations of execution flow.

Watch Out for These Misconceptions

Common Misconception

During Pair Programming: Shape Calculator Functions, watch for students who define functions but forget to call them or assume functions run automatically.

What to Teach Instead

Remind pairs to swap laptops and run each other’s code, inserting print statements right after function calls to visibly confirm execution and reinforce the need for explicit calls.

Common Misconception

During Scope Debugging Challenge, watch for assumptions that variables inside functions remain available outside their blocks.

What to Teach Instead

Have groups annotate each variable with its lifetime using color codes, then test predictions by running the code in a debugger and observing when variables disappear from the local scope.

Common Misconception

During Function Design Relay, watch for students who treat return values as optional or print them instead of using them in further calculations.

What to Teach Instead

Provide a worksheet where students must assign return values to variables before using them in the next function call, making the flow of data explicit and correcting the misconception through immediate testing.

Assessment Ideas

Exit Ticket

After Personal Code Refactor, ask students to submit both their original and refactored code alongside a brief note identifying one function they created, its parameters, and its return value (or None).

Quick Check

During Scope Debugging Challenge, circulate and ask each group to verbally explain the expected output of their code, focusing on which variables exist at each step before running it.

Discussion Prompt

After Function Design Relay, facilitate a whole-class discussion where students share one function they designed during the relay and explain why they chose its parameters and return value, linking their choices to modular design principles.

Extensions & Scaffolding

• Challenge: Ask students to extend their shape calculator by writing a function that takes three parameters (length, width, height) and returns the surface area of a rectangular prism.
• Scaffolding: Provide a partially completed function definition with missing parameters or return statements for students to fill in during the Pair Programming task.
• Deeper: Introduce nested function calls where the return value of one function becomes the argument to another, and challenge students to design a simple data processing pipeline.

Key Vocabulary

Function Definition	A block of organized, reusable code that is used to perform a single, related action. It specifies the name of the function and the sequence of statements it contains.
Function Call	The invocation of a defined function. When a function is called, the program's execution jumps to the function's code block and executes its statements.
Parameter	A variable listed inside the parentheses in the function definition. It acts as a placeholder for values that will be passed into the function when it is called.
Argument	A value that is sent to the function when the function is called. This value is assigned to the corresponding parameter within the function.
Scope	The region of a program where a variable is recognized and can be accessed. Variables can have global scope (accessible everywhere) or local scope (accessible only within a specific function).