KS3 Computer Science – Subroutines, IF/ELSE & Calculator Builder in Small Basic (2026 Updated) | FREE Online Compiler | Dyslexia-Friendly
A fully resourced, dyslexia-friendly KS3 Computer Science lesson introducing Subroutines (Sub…EndSub), branching with IF/ELSE, and creating a fully functional calculator program.
Includes a complete PowerPoint, structured worksheet, worked examples and challenge tasks — all designed for use with the FREE online Small Basic compiler, meaning zero installation issues and full compatibility with school devices.
Designed with dyslexia-friendly formatting: pastel colour schemes, readable fonts, reduced text density and high-contrast code samples to support accessibility.
Students learn:
- How subroutines work and why programmers use them
- How Sub and EndSub create reusable blocks of code
- How to call subroutines in the correct order
- How IF/ELSE statements control program decisions
- How to build structured programs such as calculators and mini-games
Practical coding tasks:
- Analyse example code to understand execution flow
- Complete a partially written calculator by creating AddNumbers(), SubtractNumbers() and MultiplyNumbers()
- Use IF/ELSE logic to choose which subroutine runs
- Integrate user input to customise calculations
- Extend the calculator with divide functionality and improved structure
Challenge activities:
- Add subroutines that collect Number1 and Number2 directly from the user
- Create a command-driven calculator where the user selects add, subtract, multiply or divide
- Wrap the entire calculator in a WHILE loop so it repeats until the user types EXIT
- Build a maths game where random numbers are generated and the user must answer correctly to continue
Assessment and evidence:
- Screenshot prompts using the Windows Snipping Tool (or equivalent)
- Written explanation boxes to check understanding of subroutines and branching
- Debugging and code-building tasks to demonstrate mastery
Lesson objectives:
- Create and call subroutines confidently
- Use IF/ELSE statements to control program flow
- Develop a working calculator using structured programming
- Apply logic, randomness and loops to create simple interactive programs
Perfect for:
- KS3 Computing
- Coding clubs and enrichment
- Introduction to structured programming
- Preparation for Python functions and selection
Classroom-ready, accessible and confidence-building — this lesson helps students think like real programmers while mastering structured code design.
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£2.50