Function Design and ReusabilityActivities & Teaching Strategies
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.
Learning Objectives
- 1Analyze existing functions to identify specific characteristics that hinder or promote reusability.
- 2Design a function that accepts parameters for all variable data, producing predictable outputs.
- 3Critique a given function's design, proposing specific modifications to improve its modularity and reusability.
- 4Compare and contrast a highly reusable function with one that has hidden dependencies or side effects.
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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.
Prepare & details
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.
Setup: Groups at tables with problem materials
Materials: Problem packet, Role cards (facilitator, recorder, timekeeper, reporter), Problem-solving protocol sheet, Solution evaluation rubric
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.
Prepare & details
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.
Setup: Groups at tables with problem materials
Materials: Problem packet, Role cards (facilitator, recorder, timekeeper, reporter), Problem-solving protocol sheet, Solution evaluation rubric
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.
Prepare & details
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.
Setup: Standard classroom seating; students turn to a neighbor
Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs
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.
Prepare & details
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.
Setup: Wall space or tables arranged around room perimeter
Materials: Large paper/poster boards, Markers, Sticky notes for feedback
Teaching This Topic
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.
What to Expect
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.
These activities are a starting point. A full mission is the experience.
- Complete facilitation script with teacher dialogue
- Printable student materials, ready for class
- Differentiation strategies for every learner
Watch Out for These Misconceptions
Common MisconceptionDuring Code Critique: Reusability Audit, watch for students who conclude a function is reusable because it appears twice in the same program.
What to Teach Instead
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.
Common MisconceptionDuring Redesign Workshop: From Brittle to Reusable, watch for students who add more parameters to make a function flexible.
What to Teach Instead
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.
Common MisconceptionDuring Think-Pair-Share: Function Portability Test, watch for students who dismiss void functions as less useful.
What to Teach Instead
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.
Assessment Ideas
After Code Critique: Reusability Audit, have students exchange their audits and challenge each other to identify one hidden dependency they missed initially.
During Redesign Workshop: From Brittle to Reusable, circulate and ask each pair to explain why their refactored function can now run in a new program without changes.
After Gallery Walk: Good and Bad Function Design, facilitate a quick class vote on the three most important principles for reusable functions, then tally results and discuss overlaps and differences.
Extensions & Scaffolding
- Challenge students who finish early to design a function that can be reused in both a game project and a data analysis project, then explain their parameter choices in a short reflection.
- For students who struggle, provide starter code that intentionally includes a global variable and ask them to refactor it using only parameters.
- Offer deeper exploration by asking students to create a mini-library of three reusable functions for a peer to use in an unfamiliar project, including clear documentation and example calls.
Key Vocabulary
| Modularity | The degree to which a system's components may be separated and recombined. In programming, this often refers to breaking down a large program into smaller, independent functions. |
| 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 when it is called. |
| Argument | The actual value that is sent to a function when it is called. This value is assigned to the corresponding parameter within the function. |
| Side Effect | Any change that a function makes to the state outside of its local environment. This can include modifying global variables or performing input/output operations. |
| Dependency | A relationship where a function relies on external factors or specific conditions to operate correctly, such as global variables or specific file structures. |
Suggested Methodologies
More in Programming with Purpose
Data Types and Variables
Students will learn to use different data types and variables to store and manipulate information in a program.
2 methodologies
Conditional Statements (If/Else)
Students will use conditional statements to control the execution flow of a program based on specific criteria.
2 methodologies
Looping Constructs (For/While)
Students will implement loops to repeat blocks of code, improving efficiency and reducing redundancy.
2 methodologies
Introduction to Functions
Students will design reusable code blocks to improve readability and maintainability.
2 methodologies
Documentation and Code Readability
Students will learn the importance of documentation in improving the usability of a code library.
2 methodologies
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