Computing · Year 2 · Creative Programming with ScratchJr · Autumn Term

Debugging ScratchJr Projects

Finding and fixing mistakes in code to make programs run as intended.

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

About This Topic

Debugging ScratchJr projects helps Year 2 pupils find and fix errors in their code so programs run as planned. They spot why a sprite moves incorrectly, test blocks one at a time, explain the problem, and change the right block. This matches KS1 Computing standards for programming and debugging, building on simple sequencing from earlier lessons.

In the Creative Programming unit, pupils practice logical steps: predict outcomes, run code, compare results, and refine. They use precise words to describe fixes, which strengthens communication and resilience. These skills link to computational thinking across the curriculum, preparing pupils for Year 3 challenges like variables.

Pupils gain most from active approaches because ScratchJr gives instant feedback on changes, turning trial and error into quick wins. Pair testing and bug hunts make spotting issues collaborative and fun, helping pupils build confidence in explaining their thinking while keeping lessons focused and engaging.

Key Questions

1. Identify what went wrong when a sprite does not move as you planned.
2. Explain why your sprite did not move the way you expected, and describe the step you changed to fix it.
3. Show how to test your ScratchJr script one block at a time to find which block caused the problem.

Learning Objectives

• Identify the specific block in a ScratchJr script that causes a sprite to behave unexpectedly.
• Explain, using precise language, why a sprite did not move as planned in a ScratchJr project.
• Demonstrate how to test a ScratchJr script block by block to isolate a programming error.
• Modify a ScratchJr script to correct a bug and make a sprite perform the intended action.

Before You Start

Sequencing Actions with ScratchJr

Why: Students need to understand how to build a basic script by arranging blocks in order before they can identify when that order is incorrect.

Basic Sprite Movement in ScratchJr

Why: Pupils must be able to use basic movement blocks (e.g., move right, move left) to recognize when a sprite is not moving as planned.

Key Vocabulary

Bug	A mistake or error in a computer program that causes it to behave incorrectly.
Debugging	The process of finding and fixing errors, or bugs, in a computer program.
Script	A sequence of instructions, represented by blocks, that tells a sprite what to do in ScratchJr.
Sprite	A character or object in a ScratchJr project that can be programmed to move and interact.

Watch Out for These Misconceptions

Common Misconception

If the program fails, delete everything and start again.

What to Teach Instead

Pupils learn systematic testing isolates single blocks. Pair discussions reveal small tweaks work best, building patience. Hands-on retesting shows quick fixes save time over restarts.

Common Misconception

Sprites guess movements if blocks are close enough.

What to Teach Instead

Exact block order matters for precise paths. Observing failed runs in small groups helps pupils see sequence errors. Collaborative fixes reinforce that code needs full detail.

Common Misconception

Bugs always hide in the last block added.

What to Teach Instead

Errors can be anywhere, so full scripts need checking. Individual step testing uncovers early issues. Group shares highlight varied bug spots, promoting thorough habits.

Active Learning Ideas

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.

25 min·Pairs

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.

35 min·Small Groups

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.

20 min·Individual

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.

30 min·Whole Class

Real-World Connections

• Video game designers, like those at Nintendo, spend a lot of time debugging their code to ensure characters move smoothly and game mechanics work correctly before a game is released.
• App developers for companies such as Duolingo use debugging techniques to find and fix errors in their applications, making sure lessons load properly and user progress is saved accurately.

Assessment Ideas

Exit Ticket

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?

Quick Check

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?'

Discussion Prompt

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?'

Frequently Asked Questions

How do you teach debugging ScratchJr to Year 2?

Start with simple buggy projects where one block fails, like wrong motion. Guide pupils to predict, run, and compare outcomes. Use think-alouds to model explaining fixes, then let them practise in pairs. This scaffolds from observation to independent correction over 2-3 lessons.

What are common Year 2 debugging errors in ScratchJr?

Pupils often overlook block order or repeat tests without changes. They may blame the app instead of code. Address with visual checklists for prediction-run-fix cycles. Regular pair reviews catch these, turning errors into teachable moments for precise language.

How can active learning help students debug ScratchJr projects?

Active methods like pair testing and bug hunts provide instant code feedback, making errors visible and fixes rewarding. Pupils discuss predictions aloud, compare real runs, and collaborate on changes, which builds reasoning skills. Whole-class demos followed by hands-on practice ensures all engage, boosting confidence and retention over passive watching.

How to assess debugging skills in Year 2 Computing?

Observe pupils testing blocks singly and explaining fixes verbally or in logs. Use success criteria: identifies error, states why it failed, changes one block, retests. Rubrics score prediction accuracy and peer teaching. Portfolios of before-after projects show progress clearly.