Image source: File:Peanut-Butter-Jelly-Sandwich.jpg (Wikimedia Commons)
Could you write instructions for making this sandwich that are so clear a robot could follow them? “Put peanut butter on the bread” sounds fine, until the robot puts the whole jar on top of the loaf! Computers are like that robot: they do exactly what they are told, nothing more.
In this post:
- What makes a good set of instructions (an algorithm)
- Solving a problem step by step
- A robot programming game
- A partner game, two more activities and a quiz
Algorithms: instructions for computers (and people)
An algorithm is a set of step-by-step instructions for doing a task. Recipes, directions to a friend’s house and the rules of a game are all algorithms. Good instructions are:
- Clear: each step means one thing only. “Spread some peanut butter” is vague; “use the knife to spread one spoonful of peanut butter on one slice” is clear.
- In the right order: you cannot spread before you open the jar!
- Complete: no steps missing.
- Finished: there is a clear end.
Watch: the exact instructions challenge
Two children write instructions for making a sandwich, and their dad follows them exactly. Watch what goes wrong, and think about how you would fix each step.
Video: Exact Instructions Challenge PB&J Classroom Friendly – Josh Darnit – https://www.youtube.com/watch?v=FN2RM-CHkuI
Solving a problem, step by step
Bigger problems need some thinking before you write the steps. Here is how a Form 1 class might plan how to raise $1,500 for a class trip:
| Step | What it means | Example |
|---|---|---|
| 1. Gather information | Find out the facts | We need $1,500 in six weeks. There are 30 of us. |
| 2. Brainstorm | List lots of ideas, even silly ones | Bake sale, car wash, movie afternoon, raffle, sponsored walk |
| 3. Identify resources | What do we need for each idea? | People, money to start, equipment, space, permission from the principal |
| 4. Weigh the pros and cons | Compare the ideas | Car wash: cheap to run, but needs water and a dry day. Bake sale: easy, but parents need to bake. |
| 5. Choose the most feasible | Pick the idea that will work best | A bake sale at lunchtime on two Fridays |
| 6. Outline the main steps | Write the plan in order | Get permission → sign-up sheet for bakers → make posters → set up table → sell → count money → hand to the form teacher |
Activity: put the steps in order
Try it: washing your hands
Use ▲ and ▼ to put these instructions in order, then click “Check my order”.
▲ First step
- Turn on the tap
- Wet your hands
- Put soap on your hands
- Scrub all over your hands for 20 seconds
- Rinse off the soap
- Turn off the tap
- Dry your hands with a clean towel
▼ Last step
Activity: program the robot
Try it: robot to the star
Build a program for the robot 🤖 by clicking the command buttons, then click Run program. The robot starts facing the way the small arrow shows. Turning does not move it: it only changes the way it faces. Then try level 2!
Your program:
Activity: spot the problem
Try it: spot the problem
Click the best answer. You get feedback straight away; only your first click counts towards your score.
1. “Go to the shop. Buy bread.” What is missing for someone who has never been there?
2. “Pour the cereal. Get a bowl. Add milk.” What is wrong?
3. “Add some sugar.” Why is this a problem for a robot?
Partner game: draw what I say
Sit back to back. Partner A gets a simple drawing made of shapes (your teacher has some) and gives instructions; Partner B draws without seeing it and without asking questions. Compare the drawings, then swap. Use this feedback form for your partner’s instructions:
| My partner’s instructions… | Yes | Sometimes | No |
|---|---|---|---|
| were clear (one meaning each) | |||
| were in a sensible order | |||
| gave sizes and positions (big, small, top left…) | |||
| had no missing steps |
Self-check quiz
Self-check quiz
Click the best answer. You get feedback straight away; only your first click counts towards your score.
1. What is an algorithm?
2. Why must instructions for a computer be exact?
3. In problem solving, what is brainstorming?
4. What does “most feasible solution” mean?
5. Which instruction is clearest?
Related posts on islandclass.org
- Computational Thinking – A simple task! (Optional Class Activity) – partner activity
- Problem Solving Discussion – the egg-drop problem
For later, in Forms 4–5 (CSEC IT): these go deeper and are for when you reach CSEC Information Technology.
Next: Getting Started with Scratch: Drawing Shapes
Syllabus link: Forms 1–3 ICT curriculum, Module 5, Objective 5.1 – outline the main steps to execute a simple activity.
Attributions to media used in this post:
- Peanut-Butter-Jelly-Sandwich.jpg – Evan-Amos – Public domain (via Wikimedia Commons)
- Video: Exact Instructions Challenge PB&J Classroom Friendly – Josh Darnit (YouTube)
Updates
2026/10/21
- Fixed the activity code so its buttons keep working.
© 2026 Vedesh Kungebeharry. All rights reserved.