Edexcel IAL Computer Science – U4.20 Run-length encoding – Lesson & Worksheet

Bespoke, fully editable lesson for Pearson Edexcel International A Level Computer Science (2026): U4.20 Run-length encoding. Slides, worksheet and full answers.

Written for Unit 4 Advanced Practical Programming, topic 21 Algorithms (specification 21.2.2). Everything is editable, so you can adapt it to your class.

What’s included

• PowerPoint lesson (16 slides) with teacher notes on every slide
• Student worksheet (Word), ready to print or edit
• Answer sheet (Word) with mark-scheme style answers for every question

U4.20 Run-length encoding

By the end of the lesson students can:

• Write a function that run-length encodes text into (character, count) pairs and a string
• Write a function that decodes run-length encoded data back to the original
• Test the round trip, and explain when RLE makes data larger

Worksheet sections: A. Recall; B. By hand; C. Amend the format; D. Exam-style questions; E. Challenge

Every lesson includes

• Learning goals and a starter question
• Clear explanations, diagrams and worked examples (Python 3 throughout, as the specification requires)
• A quick check and a “your turn” task linked to the worksheet
• Exam-style questions with marks, and an exit ticket

Format

• PowerPoint (.pptx) and Word (.docx), fully editable
• Works in PowerPoint and Google Slides
• Calm, muted sixth-form design, consistent across the whole course

These are independent resources written for the Pearson Edexcel International Advanced Level Computer Science specification (Issue 1, first teaching 2026; IAS XCP01, IAL YCP01). They are not produced or endorsed by Pearson.