Finding and Fixing Bugs (Debugging)

Active debugging builds both technical skill and a growth mindset. Students learn that errors are normal and fixable through careful observation and incremental testing. Hands-on activities like Pair Debug Challenge and Bug Hunt Stations make problem-solving visible, so pupils see debugging as a puzzle to solve, not a failure to avoid.

• Year 3
• Computing
• 4 activities
• 20 min–45 min

Learning Objectives

1. Identify specific code blocks that cause a sprite to behave unexpectedly.
2. Explain why testing code incrementally helps in locating errors.
3. Analyze the impact of a single incorrect code block on a sprite's sequence of actions.
4. Evaluate strategies for remaining calm and persistent when debugging code.
5. Justify the importance of errors as learning opportunities in programming.

Escape Room

⏱ 30 min·Pairs

Pair Debug Challenge: Sprite Maze

Provide buggy code for a sprite to navigate a maze. Pairs predict what will happen, run the code, note the exact failure point, and fix one block at a time. They swap with another pair to test fixes and explain changes.

Prepare & details

Justify why 'failing' is a vital part of the programming process.

Facilitation Tip: During Pair Debug Challenge, circulate and ask each pair to explain one bug they found and how they fixed it before moving to the next maze.

Setup: Group tables with puzzle envelopes, optional locked boxes

Materials: Puzzle packets (4-6 per group), Lock boxes or code sheets, Timer (projected), Hint cards

• Remember
• Apply
• Analyze
• Relationship Skills
• Self-Management

Escape Room

⏱ 45 min·Small Groups

Bug Hunt Stations: Code Cards

Set up stations with printed code snippets on cards showing common errors like wrong sequences or loops. Small groups test each on devices, circle the bug, and rewrite correctly. Rotate stations and share one fix per group.

Prepare & details

Analyze strategies to isolate a single block of code causing a bug.

Facilitation Tip: At Bug Hunt Stations, provide colored stickers so students can mark code blocks they tested and mark the ones still in question.

Setup: Group tables with puzzle envelopes, optional locked boxes

Materials: Puzzle packets (4-6 per group), Lock boxes or code sheets, Timer (projected), Hint cards

• Remember
• Apply
• Analyze
• Relationship Skills
• Self-Management

Escape Room

⏱ 20 min·Whole Class

Whole Class Debug Demo: Live Prediction

Project a buggy sprite program. Class predicts behaviour, you run it to reveal the bug, then vote on fixes. Implement student ideas live, discuss why each works or fails, and log strategies on a shared board.

Prepare & details

Evaluate different approaches to staying calm when code does not work as expected.

Facilitation Tip: In Whole Class Debug Demo, pause after each prediction and ask two students to share their expected outcome before running the code to surface misconceptions early.

Setup: Group tables with puzzle envelopes, optional locked boxes

Materials: Puzzle packets (4-6 per group), Lock boxes or code sheets, Timer (projected), Hint cards

• Remember
• Apply
• Analyze
• Relationship Skills
• Self-Management

Escape Room

⏱ 25 min·Individual

Individual Test Log: Personal Program

Students create a simple sprite dance, introduce a deliberate bug, then log tests: prediction, outcome, change made. They repeat until fixed, reflecting on patterns in their errors.

Prepare & details

Justify why 'failing' is a vital part of the programming process.

Facilitation Tip: In Individual Test Log, model how to write a concise prediction line like ‘Sprite will move 10 steps right’ before testing, so students see the value of clear expectations.

Setup: Group tables with puzzle envelopes, optional locked boxes

Materials: Puzzle packets (4-6 per group), Lock boxes or code sheets, Timer (projected), Hint cards

• Remember
• Apply
• Analyze
• Relationship Skills
• Self-Management

Teaching This Topic

Teach debugging as a routine, not a reaction. Model your own thinking aloud when bugs appear, showing how you predict, test, and adjust. Avoid fixing student code for them; instead, ask guiding questions like ‘What did you expect to happen?’ and ‘Where could the first mistake be?’ Research shows that students who verbalize their process before running code catch more errors and build stronger debugging habits.

What to Expect

By the end of these activities, students will confidently test code step by step, predict outcomes, and isolate bugs with calm persistence. They will move from random guesses to systematic fixes, using tools like prediction logs and code cards to guide their work.

Watch Out for These Misconceptions

Common Misconception

During Pair Debug Challenge, watch for students who erase entire code or restart without testing each block first.

What to Teach Instead

Pause the activity and remind pairs to use the step-by-step run feature to test one block at a time, marking each as working or not before making any changes.

Common Misconception

During Bug Hunt Stations, watch for students who change code randomly until something works.

What to Teach Instead

Ask students to write a prediction for each card before testing, then circle the exact block that caused the mismatch between prediction and outcome.

Common Misconception

During Whole Class Debug Demo, watch for students who blame the computer or the software for the bug.

What to Teach Instead

Point to the code on the board and ask the class to read it aloud together, emphasizing that the computer did exactly what the instructions said, so the error must be in the human-written code.

Assessment Ideas

Quick Check

After Pair Debug Challenge, provide a new simple sprite program with one bug and ask students to run it, circle the bug, and write the correct code block on a sticky note to share with their partner.

Discussion Prompt

During Whole Class Debug Demo, ask students to share three steps they would take to find a bug causing an endless loop, recording their ideas on the board under the categories ‘Predict’, ‘Test’, and ‘Fix’.

Exit Ticket

After Individual Test Log, give each student a card with the statement ‘When my code doesn’t work, I feel…’ and ask them to complete the sentence and write one strategy they can use to stay calm and keep trying, such as ‘I will run the code step by step’.

Extensions & Scaffolding

• Challenge: Provide a maze with multiple bugs (e.g., incorrect direction, missing repeat, wrong event trigger) and ask students to document every fix and test in their log.
• Scaffolding: Give students a partially completed test log with sentence starters such as ‘I expected the sprite to… but it… so I…’ to help them articulate their process.
• Deeper exploration: Introduce conditional statements with bugs, such as a sprite that should change color only when touching a wall, and ask students to design a test plan with at least three test cases.

Key Vocabulary

bug	An error or fault in a computer program that causes it to produce an incorrect or unexpected result, or to behave in unintended ways.
debugging	The process of finding and fixing errors, or bugs, in computer code.
sequence	A set of instructions that are followed in a specific order to achieve a result.
loop	A programming structure that repeats a sequence of instructions until a specific condition is met.
test	To run a program or part of a program to check if it works correctly and to find any bugs.