Sequences and Loops — Year 3 Lesson Plan
National Curriculum: Computing KS2 — design, write and debug programs that accomplish specific goals; use sequence, selection and repetition in programs
Overview
Pupils extend their programming knowledge by learning to use loops to repeat sections of code efficiently. They compare writing a sequence of repeated commands with using a loop, understand the concept of a count-controlled loop, and apply this in a visual programming environment such as Scratch to create animations or patterns.
Learning Objectives
- Explain what a loop is and why it is useful in programming.
- Use a count-controlled loop to repeat a block of code a set number of times.
- Compare a looped program with a repeated sequence and explain the benefits.
- Design and create a program that uses sequences and loops to achieve a goal.
Key Vocabulary
Suggested Lesson Structure
Show a Scratch program that draws a square using 8 individual move/turn blocks vs. the same result using a loop block (repeat 4). Ask: what is the same? What is different? Which would you prefer to write and why?
Introduce the concept of a loop: code that repeats. In Scratch, demonstrate the 'Repeat' block. Build a square step by step: move 100 steps, turn 90 degrees — repeat 4 times. Then introduce an infinite loop (the 'forever' block): useful for animations. Challenge: can they use a loop to draw a hexagon? (repeat 6, turn 60 degrees). Discuss: how does a loop make code shorter and easier to change?
Pupils open a starter Scratch project. Task: use a repeat loop to make a sprite bounce back and forth 5 times, then stop. Teacher checks understanding: how many iterations will there be? What happens inside the loop?
Pupils design and build their own looped animation in Scratch: a sprite that draws a repeated pattern or performs a repeated action. They must use at least one count-controlled loop and annotate their code with comments explaining what the loop does.
Pair share: show your program and explain one loop you used. Class discussion: when might an infinite loop be useful? When would it be a problem? Connect to real life: the operating system on a computer uses loops constantly — checking for input, updating the screen.
Common Misconceptions
- Pupils often think loops always repeat forever — count-controlled loops repeat a fixed number of times and then stop.
- Forgetting that the code inside the loop runs each iteration — if the loop repeats 4 times, each block inside runs 4 times.
Prior Knowledge
Pupils should already be able to:
- Experience creating sequences of instructions in a programming environment.
- Familiarity with Scratch or similar block-based programming tools.
- Understanding of what an algorithm and a sequence are.
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