What Is an Algorithm? — Year 1 Lesson Plan
National Curriculum: Computing KS1 — understand what algorithms are; how they are implemented as programs on digital devices; that programs execute by following precise and unambiguous instructions
Overview
Pupils are introduced to the concept of an algorithm as a precise set of instructions for completing a task. Through unplugged activities — instructing a partner to make a sandwich, draw a shape, or navigate a grid — they discover why instructions must be clear, ordered, and unambiguous before they can be followed by a computer.
What Is an Algorithm? learning objectives
- Explain what an algorithm is in simple terms.
- Give a set of instructions that achieves a specific outcome.
- Understand that algorithms must be precise and in the correct order.
- Recognise that computers follow algorithms exactly as written.
Success criteria
- I can say what an algorithm is.
- I can give instructions in the right order.
- I can spot when an instruction is not clear enough.
- I can explain that a computer does exactly what it is told.
Key Vocabulary
Suggested Lesson Structure
Ask a volunteer to be a 'robot'. Give intentionally vague instructions: 'Get the book.' Robot stands still. Why? Discuss that robots and computers need very precise instructions — they cannot guess what you mean.
Introduce the word 'algorithm'. Explain that an algorithm is like a recipe: a precise list of steps in the right order. Demo: algorithm for making a jam sandwich. Each step must be clear. Ask: what happens if the steps are in the wrong order? Work through a simple grid navigation: pupils give step-by-step instructions (move forward, turn right) to move a class toy from A to B. Connect to computers: 'When we write a program, we are writing an algorithm the computer will follow.'
Pupils work in pairs. One is the 'robot', one is the 'programmer'. The programmer writes an algorithm (on a strip card) to draw a simple shape — a square — step by step. Robot follows instructions exactly. Swap roles. Discuss: what went wrong? Why?
Pupils write their own algorithm for a daily task (washing hands, making toast, getting dressed) in at least five numbered steps. They swap with a partner who checks: is it clear? Is it in the right order? Could a robot follow it?
Share one algorithm. Class identifies if any steps are missing or unclear. Reinforce: a computer follows algorithms exactly — no more, no less. Computers are fast but they are not clever.
Support and extension for what is an algorithm?
Support
- Use picture instruction cards to put in order (for example brushing teeth).
- Work with an adult as the “robot” so pupils can test one instruction at a time.
- Limit instructions to forward, turn left and turn right.
Extension
- Write an algorithm for a partner to draw a simple shape without seeing it.
- Find and fix a mistake (debug) in a set of instructions.
- Program a floor robot such as a Bee-Bot to follow their algorithm.
Check for understanding
Quick questions for the plenary or an exit ticket. Tap a question to see the answer.
1. What is an algorithm?
Answer: A set of clear instructions, in order, to do a job.
2. Why does the order of instructions matter?
Answer: If the steps are in the wrong order, the job goes wrong, like putting shoes on before socks.
3. What does a computer do if an instruction is wrong?
Answer: It follows it exactly, even if the result is wrong.
4. Make this instruction more precise: “Go over there.”
Answer: For example “Take three steps forward, then turn left.”
Resources you will need
- Picture sequencing cards
- Floor robots such as Bee-Bots, if available
- A simple grid mat drawn on the floor or on paper
Common Misconceptions
- Pupils often think algorithms are only for computers — algorithms exist everywhere: recipes, instructions, and routines are all algorithms.
- Thinking that a rough description is enough — algorithms require precision; 'put the bread in the toaster' is not precise enough if you haven't specified which bread.
Prior Knowledge
Pupils should already be able to:
- Experience of following and giving instructions in everyday life.
- No prior computing experience required — this is typically the first formal computing lesson.
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