Computer Science · 9th Grade

Active learning ideas

Function Design and Reusability

Students learn best when they actively apply design principles rather than absorb them passively. For function reusability, this means evaluating messy code, redesigning flawed implementations, and testing portability. These hands-on experiences help students see how small design choices affect whether code can move between projects without breaking.

• Common Core State Standards
• CSTA: 3A-AP-17
• CSTA: 3A-AP-18

• 20–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Collaborative Problem-Solving
• 30 min · Individual

Code Critique: Reusability Audit

Each student receives a function (drawn from a shared pool) and evaluates it against a four-criteria rubric: specific purpose, clear parameter names, predictable output, and no global dependencies. Students annotate directly on printed code, then share one finding with the class.

Analyze what makes a function truly reusable across different projects.

Facilitation Tip

During Code Critique: Reusability Audit, assign each student a different function to audit and prepare three specific observations before sharing with a partner.

What to look for

Provide students with two functions: one designed for reusability and one with hidden dependencies. Ask students to work in pairs to identify the strengths and weaknesses of each function regarding reusability, then write one sentence explaining which function is more reusable and why.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 02

• Collaborative Problem-Solving
• 45 min · Small Groups

Redesign Workshop: From Brittle to Reusable

Groups receive a function that works but is not reusable (hardcoded filenames, global variable use, inconsistent return behavior). They redesign it for reusability, documenting the changes they made and why. Groups present before and after versions with an explanation of each design decision.

Design a function with clear inputs and outputs for maximum reusability.

Facilitation Tip

In Redesign Workshop: From Brittle to Reusable, require students to write a one-sentence purpose statement for their function before they begin editing, then compare it to their final version.

What to look for

Present a function that performs a common task but relies on a global variable. Ask students to rewrite the function to accept the necessary information as a parameter, explaining in one sentence why this change improves reusability.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 03

• Think-Pair-Share
• 20 min · Pairs

Think-Pair-Share: Function Portability Test

Students describe a function they wrote, then their partner tries to describe a new context where that function could be used without modification. If the partner cannot find one, the pair identifies what would need to change to make the function portable.

Critique existing functions for their reusability and modularity.

Facilitation Tip

For Think-Pair-Share: Function Portability Test, have students run their function in a completely new file before the pair discussion so they experience firsthand what breaks.

What to look for

Pose the question: 'Imagine you are building a library of functions for other students to use. What are the top three principles you would follow to ensure your functions are easy for them to understand and reuse in their own projects?' Facilitate a brief class discussion to share ideas.

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

Activity 04

• Gallery Walk
• 30 min · Small Groups

Gallery Walk: Good and Bad Function Design

Post eight function examples, four with strong reusability and four with specific reusability problems. Students label each as reusable or not reusable with a one-sentence justification and a suggested fix for the problematic ones.

Analyze what makes a function truly reusable across different projects.

Facilitation Tip

During Gallery Walk: Good and Bad Function Design, ask students to attach a sticky note to each displayed function showing one improvement they would make.

What to look for

Provide students with two functions: one designed for reusability and one with hidden dependencies. Ask students to work in pairs to identify the strengths and weaknesses of each function regarding reusability, then write one sentence explaining which function is more reusable and why.

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

A few notes on teaching this unit

Start by normalizing failure with examples of ‘broken’ functions that seem to work in one program but fail in another. Use side-by-side comparisons to build intuition about hidden dependencies. Teach students to ask, ‘What assumptions does this function make?’ before asking, ‘Does it work?’ Research shows that students grasp abstraction better when they refactor concrete examples rather than discuss abstract principles.

Successful learners will recognize dependencies, justify parameter choices, and revise functions to remove hidden assumptions. They will explain why clarity and specificity matter more than cleverness or extra features in reusable functions.

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Watch Out for These Misconceptions

• During Code Critique: Reusability Audit, watch for students who conclude a function is reusable because it appears twice in the same program.

  Prompt them to copy the function into a clean file and test it. If it fails due to hard-coded file paths or global variables, they will see that true reusability requires no hidden dependencies.

• During Redesign Workshop: From Brittle to Reusable, watch for students who add more parameters to make a function flexible.

  Ask them to rewrite the function’s purpose in one sentence. If it can’t be stated clearly, too many parameters likely reflect an overly broad task.

• During Think-Pair-Share: Function Portability Test, watch for students who dismiss void functions as less useful.

  Have them classify functions by their output type and discuss when no return value is appropriate, such as for in-place sorting or file writing.

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Methods used in this brief

• Collaborative Problem-Solving
• Think-Pair-Share
• Gallery Walk