Python Debugging & Code Tracing | KS3 & GCSE

Help pupils practise Python debugging and code tracing with 30 structured activities for KS3 and GCSE Computer Science. Includes printable worksheets, trace tables, optional hints, worked answers and Python files.

Created by Pixel & Python, this pack is designed for Years 9 and 10 pupils who have already encountered basic Python programming. It provides focused practice in reading code, identifying errors, explaining corrections and checking results.

A confused snack machine, an unstoppable robot and a ticket desk with two faults bring a little personality to the classroom while keeping the focus on programming.

What’s included

20 debugging activities covering syntax errors, runtime errors and logic errors

10 code-tracing activities with structured trace tables and output prediction

A two-page diagnostic assessment with answers and suggested follow-up activities

Foundation, Developing and Stretch tasks

Two graduated hints for each debugging activity

Extension questions with teacher answers

An exit check and pupil reflection sheet

Teacher guidance, suggested timings, an activity map and assessment criteria

Python topics covered

Activities explore variables, assignment, input and type conversion, comparison operators, selection, Boolean logic, for loops, while loops and range endpoints.

Further tasks cover running totals, list indexing, list methods, string handling, functions, parameters, return values, integer division, remainders, nested loops, sentinel values and finding a maximum.

How pupils use the activities

Each debugging worksheet gives pupils a clear requirement and a short faulty program. They identify the problem, explain its cause, write a repair and complete a test table.

The tracing worksheets ask pupils to follow changing values, predict the exact output and explain how a change would affect the program. This gives teachers evidence of pupils’ understanding beyond whether their code runs.

Flexible classroom use

Choose individual activities for starters, homework, retrieval practice or intervention. Combine related tasks for a longer lesson, or use familiar topics for cover work.

Most tasks have suggested timings of approximately 8 to 20 minutes, with additional time available for extensions and discussion. Pupils can work independently or in pairs. Printable activities can also be completed through manual tracing without a computer.