Introduction to Functions

Functions help students move from writing linear scripts to designing systems where code is organized, reusable, and easier to debug. Active learning works for this topic because students see firsthand how breaking tasks into functions improves clarity and reduces repetition.

• 9th Grade
• Computer Science
• 4 activities
• 25 min–40 min

Learning Objectives

1. Explain the benefits of using functions to organize code for improved readability and maintainability.
2. Construct a simple function in Python that performs a specific, well-defined task.
3. Differentiate between parameters and arguments when defining and calling Python functions.
4. Analyze a given code snippet and refactor it by introducing functions to reduce redundancy.
5. Evaluate the clarity and efficiency of different function designs for a given problem.

Think-Pair-Share

⏱ 25 min·Pairs

Think-Pair-Share: Function Identification

Present a 40-line program written without functions. Students individually identify at least three sections they would extract into named functions and choose a name for each. Pairs compare their choices and discuss where their extractions differ. The class builds a consensus version on the board.

Prepare & details

Explain the benefits of using functions to organize code.

Facilitation Tip: During Think-Pair-Share: Function Identification, circulate and listen for students to articulate how a function’s name and purpose connect to its role in the program.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Jigsaw

⏱ 40 min·Small Groups

Collaborative Refactoring: From Script to Functions

Groups receive a working but repetitive script. Their task is to refactor it using functions without changing its output. Groups present their refactored version and explain each design choice. The class discusses which grouping strategies produced the clearest code.

Prepare & details

Construct a simple function that performs a specific task.

Facilitation Tip: In Collaborative Refactoring: From Script to Functions, emphasize naming conventions by asking students to defend their chosen function names during group discussions.

Setup: Flexible seating for regrouping

Materials: Expert group reading packets, Note-taking template, Summary graphic organizer

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

Peer Teaching

⏱ 30 min·Pairs

Peer Teaching: Function Explanation Challenge

One partner writes a function and then explains it to their partner using only plain English, no code or technical jargon. The listening partner codes what they hear described. They compare the coded result to the original and discuss any gaps in the explanation.

Prepare & details

Differentiate between parameters and arguments in function calls.

Facilitation Tip: For Peer Teaching: Function Explanation Challenge, provide sentence stems like 'This function does ____ by ____' to scaffold explanations.

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

Gallery Walk

⏱ 25 min·Small Groups

Gallery Walk: Function Anatomy

Post six function examples with different structures (no parameters, multiple parameters, return value, no return value, calling another function, modifying a list). Students annotate each with what the function does, what goes in, and what comes out.

Prepare & details

Explain the benefits of using functions to organize code.

Facilitation Tip: During Gallery Walk: Function Anatomy, assign roles so some students focus on tracing execution while others analyze parameter usage.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Teaching This Topic

Teachers should introduce functions as tools for abstraction, not just repetition. Avoid teaching functions in isolation; instead, connect them to real-world systems like vending machines or traffic lights. Research suggests students grasp functions best when they first experience the pain of repeated code, then see functions as the solution. Emphasize naming and purpose early, as these habits prevent later confusion.

What to Expect

By the end of these activities, students will define functions with parameters, call them correctly, and explain why functions make code more maintainable. They will also evaluate peers' functions for readability and correctness.

Watch Out for These Misconceptions

Common Misconception

During Think-Pair-Share: Function Identification, watch for students who claim functions are only useful when code repeats.

What to Teach Instead

Use the activity to highlight how function names like validate_user_age() improve readability even if the code runs once. Ask students to compare scripts with and without functions to see the difference in clarity.

Common Misconception

During Collaborative Refactoring: From Script to Functions, watch for students who think defining a function runs the code immediately.

What to Teach Instead

During the activity, have students annotate their scripts to mark when the function is defined versus when it is called. Ask them to trace execution step-by-step in pairs.

Common Misconception

During Peer Teaching: Function Explanation Challenge, watch for students who confuse functions with methods.

What to Teach Instead

Use this activity to clarify that methods are functions tied to objects. Ask students to identify which functions in their examples could be methods if they belonged to a class.

Assessment Ideas

Quick Check

After Think-Pair-Share: Function Identification, display a script with repeated code. Ask students to identify the repeated block and rewrite it as a function. Collect responses to check if they correctly define and call the function.

Exit Ticket

After Collaborative Refactoring: From Script to Functions, ask students to write a function call using a provided parameterized function and explain the difference between the parameter and argument in one sentence.

Peer Assessment

During Gallery Walk: Function Anatomy, have students exchange their refactored functions and use a checklist to review clarity, correctness, and parameter usage. Collect feedback forms to assess their ability to evaluate peers' work.

Extensions & Scaffolding

• Challenge: Ask students to write a program that uses nested functions to solve a multi-step problem, such as converting temperatures between Celsius and Fahrenheit and then formatting the output.
• Scaffolding: Provide a partially completed function with missing parameters or calls, and ask students to fill in the gaps using a given script.
• Deeper exploration: Introduce scope by having students experiment with local and global variables in functions, then predict and test outcomes.

Key Vocabulary

Function	A named block of code designed to perform a specific task. Functions allow code to be reused without repetition.
Parameter	A variable listed inside the parentheses in a function definition. It acts as a placeholder for a value that will be passed into the function.
Argument	A value passed to a function when it is called. This value is assigned to the corresponding parameter within the function.
Call	The act of executing a function. When a function is called, its code block runs, and it can receive arguments.
Return Value	The value that a function sends back to the part of the program that called it. Not all functions return a value.