Debugging and Error Handling

Debugging and error handling require hands-on practice because students must experience the frustration of errors to understand why systematic approaches work. Active learning through collaborative and iterative tasks builds resilience and confidence, turning debugging from a guessing game into a structured problem-solving skill.

• Grade 9
• Computer Science
• 4 activities
• 20 min–45 min

Learning Objectives

1. Differentiate between syntax errors and logical errors in a given code snippet.
2. Design a systematic debugging plan to identify and correct errors in a faulty algorithm.
3. Evaluate the effectiveness of different debugging strategies for specific error types.
4. Justify the necessity of comprehensive testing in software development using examples.

Problem-Based Learning

⏱ 30 min·Pairs

Pairs: Buggy Code Relay

Pairs get code with 3-5 deliberate errors. One partner traces execution aloud while the other notes issues; they switch to propose and test fixes using print statements. Document the process in a shared log before verifying with sample inputs.

Prepare & details

Differentiate between syntax errors and logical errors in code.

Facilitation Tip: For Buggy Code Relay, provide each pair with a different buggy snippet and a timer to keep the relay moving, ensuring all students engage in rapid, focused debugging.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

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

Problem-Based Learning

⏱ 45 min·Small Groups

Small Groups: Algorithm Debug Stations

Set up 4 stations with pseudocode or flowcharts containing syntax or logic errors. Groups spend 8 minutes per station: identify error type, fix it, test with 3 inputs, and explain to the next group. Rotate and compare fixes.

Prepare & details

Design a systematic approach to debugging a faulty algorithm.

Facilitation Tip: During Algorithm Debug Stations, set up each station with a unique error type and require groups to document their findings on a shared tracking sheet before rotating.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

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

Problem-Based Learning

⏱ 25 min·Whole Class

Whole Class: Error Prediction Challenge

Display a faulty program on screen. Class predicts outputs for given inputs, then runs it to reveal discrepancies. Discuss as a group, vote on fixes, test top ideas, and refine based on results.

Prepare & details

Justify the importance of thorough testing in the development process.

Facilitation Tip: For the Error Prediction Challenge, ask students to vote on the most likely error type before running the code, then compare predictions to actual outcomes to highlight gaps in reasoning.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

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

Problem-Based Learning

⏱ 20 min·Individual

Individual: Debug Journal Practice

Students select a past algorithm, reproduce an error with new inputs, apply a checklist (trace, isolate, test), fix it, and journal steps with before-after screenshots.

Prepare & details

Differentiate between syntax errors and logical errors in code.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

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

Teaching This Topic

Teachers should model debugging aloud, thinking through their own errors in real time to normalize mistakes and reduce frustration. Avoid rushing to provide fixes; instead, guide students with questions like 'What did you expect this line to do?' or 'How could you test if this variable holds the right value?' Research shows that students who verbalize their reasoning while debugging develop stronger metacognitive skills.

What to Expect

By the end of these activities, students will confidently distinguish between syntax and logic errors, apply step-by-step debugging methods, and justify their fixes with evidence. They will also recognize that thorough testing is essential to uncover hidden flaws before code reaches users.

Watch Out for These Misconceptions

Common Misconception

During Buggy Code Relay, watch for students making random changes to code without tracing its execution or testing inputs.

What to Teach Instead

Pause the relay and ask partners to trace one line at a time together, recording variable values after each step to identify where the output first deviates from expectations.

Common Misconception

During Algorithm Debug Stations, watch for students assuming logical errors are minor and only fixing syntax to 'make it run'.

What to Teach Instead

Require groups to test their fixed code with at least three different inputs, including edge cases, and justify why their solution addresses the logic flaw rather than just the syntax.

Common Misconception

During Error Prediction Challenge, watch for students dismissing logical errors because the code runs without crashing.

What to Teach Instead

After the vote, run the code with predicted inputs and ask students to compare outcomes to their predictions, prompting them to re-evaluate whether 'running code' equals 'correct code'.

Assessment Ideas

Quick Check

After Buggy Code Relay, present a new pair of snippets (one syntax error, one logic error) and ask students to identify the error type and explain the difference using the relay's systematic approach as evidence.

Peer Assessment

During Algorithm Debug Stations, have students swap stations halfway through and review another group’s documented fixes, checking if the solution addresses the error without introducing new issues.

Exit Ticket

After Error Prediction Challenge, ask students to outline their debugging process for a program that outputs the wrong average, including at least two specific steps they would take to verify the logic.

Extensions & Scaffolding

• Challenge: Have students create their own buggy snippet with a hidden logical error, then swap with peers to debug and document the process.
• Scaffolding: Provide a checklist of common syntax errors (e.g., missing colons, parentheses) for students to reference during individual work.
• Deeper exploration: Introduce boundary testing, where students design input sets to stress-test logical conditions, such as negative numbers or edge cases.

Key Vocabulary

Syntax Error	An error in the structure or spelling of a program's code that violates the rules of the programming language, preventing the code from running.
Logical Error	An error in a program's logic that causes it to run but produce incorrect or unexpected results, despite having correct syntax.
Debugging	The process of finding and fixing errors, or 'bugs', within computer code or algorithms.
Testing	The process of executing a program or algorithm with specific inputs to verify that it behaves as expected and to uncover errors.
Trace Table	A table used to track the values of variables throughout the execution of an algorithm or program, helping to identify logical errors.