Computing · Year 2

Active learning ideas

Debugging ScratchJr Projects

Children learn debugging best by doing it, not just watching. When Year 2 pupils actively hunt for and fix bugs in ScratchJr, they connect problem-solving to real steps they can see and change. This hands-on practice builds logical thinking and resilience because each small fix makes the program work as intended.

• National Curriculum Attainment Targets
• KS1: Computing - Programming
• KS1: Computing - Debugging

• 20–35 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Numbered Heads Together
• 25 min · Pairs

Pair Debug Challenge: Sprite Path Fix

Provide pairs with a ScratchJr project where a sprite takes a wrong path. One pupil predicts the run, the other tests block by block and notes differences. They discuss, fix one block, and retest before swapping roles.

Identify what went wrong when a sprite does not move as you planned.

Facilitation Tip

During Pair Debug Challenge, move between pairs to listen for clear descriptions of the bug and the fix before they change any blocks.

What to look for

Provide students with a pre-made ScratchJr project that has one clear bug (e.g., a sprite moving the wrong way). Ask them to write down: 1. What is the bug? 2. Which block caused the bug? 3. How did you fix it?

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

Activity 02

• Numbered Heads Together
• 35 min · Small Groups

Bug Hunt Relay: Small Group Edition

Divide class into small groups. Project three buggy scripts; groups race to identify one error per script by testing on tablets. Each pupil records the wrong behaviour and suggested fix on a group sheet.

Explain why your sprite did not move the way you expected, and describe the step you changed to fix it.

Facilitation Tip

In Bug Hunt Relay, time each small group’s turn so they focus on testing a single block sequence rather than rushing through the whole script.

What to look for

Observe students as they work on their projects. Ask targeted questions like: 'What did you expect that block to do?' 'What actually happened?' 'How can you test just that one block to see what it's doing?'

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

Activity 03

• Numbered Heads Together
• 20 min · Individual

Step-by-Step Solo Tester: Motion Bugs

Pupils load a personal project with planted errors. They run the full script, then test blocks singly, circling the problem block and writing one sentence on the fix before running again to check.

Show how to test your ScratchJr script one block at a time to find which block caused the problem.

Facilitation Tip

For Step-by-Step Solo Tester, provide printed block icons so pupils physically move them to retest logic without touching the screen.

What to look for

Show a simple ScratchJr script with a common error on the main screen. Ask: 'What do you think is wrong with this script?' 'How could we find out for sure which block is causing the problem?' 'What words can we use to describe the mistake?'

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

Activity 04

• Numbered Heads Together
• 30 min · Whole Class

Whole Class Debug Demo: Story Fail

Show a class story project that glitches. Pupils call out predictions, vote on problem blocks, then watch step-by-step testing. Class suggests and tests one collective fix.

Identify what went wrong when a sprite does not move as you planned.

Facilitation Tip

In Whole Class Debug Demo, pause after each fix to ask the class what words they would use to describe the mistake to a friend.

What to look for

Provide students with a pre-made ScratchJr project that has one clear bug (e.g., a sprite moving the wrong way). Ask them to write down: 1. What is the bug? 2. Which block caused the bug? 3. How did you fix it?

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

A few notes on teaching this unit

Teachers should model slow, verbal debugging while thinking aloud. Avoid rushing to solutions because that teaches pupils to guess rather than test. Use consistent language like ‘expected behavior’ and ‘actual behavior’ to build a shared vocabulary. Research shows young children debug more effectively when they can physically manipulate blocks and see immediate effects, so pair on-screen testing with off-screen planning.

By the end of these activities, pupils will confidently identify incorrect blocks, explain why they cause errors, and apply targeted fixes. They will explain their debugging steps to peers and self-check their work before sharing finished projects.

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Watch Out for These Misconceptions

• During Pair Debug Challenge, watch for pupils who restart the whole project instead of isolating the error.

  Remind pairs to use the printed block reference sheet to mark each tested block with a sticker, showing progress one block at a time.

• During Bug Hunt Relay, watch for pupils who assume the last added block is always the problem.

  Have the group physically reorder their tested blocks on the sheet to prove that early blocks can fail too, reinforcing thorough checking.

• During Step-by-Step Solo Tester, watch for pupils who change blocks without explaining why the original block failed.

  Ask each pupil to write a one-sentence explanation on a sticky note before they touch the screen, using the words ‘expected’ and ‘actual’.

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Methods used in this brief

• Numbered Heads Together