Teacher Notes — Week 5

Theme: Loops & Iteration
Focus Concept: Loops and Game Mechanics
Mini-Project: Barrel Jumper

Learning Objectives

  • Pupils understand what a loop is and can recognise different types (repeat, for, while, forever).
  • Pupils know that an iteration is one pass through a loop.
  • Pupils can explain how timing (pause, millis) controls loop speed.
  • Pupils use loops to move sprites, check collisions, and keep score in a simple game.

Part 1: PRIMM — Loop Showcase (≈30 min)

Predict (5)

Explain that the program below shows four loop styles and timing with millis(). Ask:

  • Which blocks look like they repeat?
  • Which loop will stop by itself? Which might run forever?
  • What will happen first when we run it?

Run (5)

Run each section and talk as you go.

A) repeat countdown

on start
    set counter to 5
    repeat 6 times
        show number counter
        set counter to counter - 1
        pause (500) ms
    show arrow west

B) for loops (grid fill)

for x from 0 to 4
    for y from 0 to 4
        plot x y
        pause (50) ms

C) while + break timed by millis()

set timer to millis()
while true
    // do something simple so pupils can see it looping
    toggle (0,0)
    pause (100) ms

    set stopTimer to millis()
    if stopTimer > timer + 5000 then
        break

D) forever

forever
    show icon Heart
    pause (200) ms
    show icon SmallHeart
    pause (200) ms

Investigate (10)

  • Loop = repeats code automatically.
    • repeat / for → fixed number of times or across a range.
    • while → repeats while a condition is true; stop with break.
    • forever → never stops; great for a game loop.
  • Iteration = one trip around the loop.
  • millis() = micro:bit’s clock (ms since start). Compare values to time things.

Child-friendly analogy: a loop is like a song on repeat; break is pressing stop.

Modify (5–7)

  • Change repeat counts and pause times.
  • Swap repeat for while and add your own stop condition.
  • Time a 3-second effect using millis().

Make (5)

  • Create a short animation using a nested for.
  • Add a sound each iteration.

Part 2: Project — Barrel Jumper (≈45–50 min)

Overview

First micro:bit game: a player sprite jumps to avoid a moving barrel.
Uses a forever game loop, collision detection, score, and optional speed-up and sound.

Step 1 — Setup

on start
    set jumper to create sprite at x: 0 y: 4
    set barrel to create sprite at x: 4 y: 4
    set score to 0
    set speed to 200   // bigger = slower; we’ll reduce this to speed up

Step 2 — Jump action (two repeat loops)

on button B pressed
    repeat 4 times
        change y by -1
        pause (100) ms
    repeat 4 times
        change y by +1
        pause (100) ms

Step 3 — Game loop (forever): move, bounce, collide

forever
    barrel move by 1
    barrel if on edge, bounce
    pause (speed) ms

    if jumper touching barrel then
        game over
        show string "Score:"
        show number score

    if barrel x = 0 then   // barrel reached the left edge
        change score by 1
        change speed by -10   // make game gradually harder

Extensions (pick & mix)

  • Add sound on jump / score / game over.
  • Add a second barrel or randomise start side.
  • Add a timer with millis() and show survival time at the end.

Vocabulary Focus (with pupil-friendly wording)

  • Loop — instructions that repeat automatically.
    • repeat / for: run a fixed number of times or across a range.
    • while: keep going while a rule is true (stop with break).
    • forever: never stops; great for the game loop.
  • Iteration — one trip around the loop.
  • Timer / millis() — the micro:bit’s clock in milliseconds; use it to time things.
  • Variable — a labelled box that stores values like score, speed, x, y.
  • Sprite — a movable object on the LED grid (player or obstacle).
  • Collision detection — checking if two sprites touch.

Differentiation

  • New coders: build base game (jump + collision).
  • Confident: add score and speed-up.
  • Stretch: add millis() timer, sounds, or multiple barrels.

Assessment

  • Can pupils name two loop types and explain when to use them?
  • Can they describe how pause/speed changes difficulty?
  • Does their game loop correctly move the barrel and detect collisions?

Troubleshooting

  • Too fast: increase pause (speed).
  • Sprites missing: check coordinates are 0–4.
  • No jump: both repeat blocks must be inside the button event.
  • No score: ensure the edge check uses barrel x = 0.

Materials & Setup

  • BBC micro:bits + USB cables
  • Chromebooks with internet access
  • Optional: headphones/speakers for sound

Safety & Safeguarding

  • Keep cables tidy and volume sensible.
  • Encourage turn-taking and pair support.

Reflection (for leader)

  • Who can clearly explain repeat vs while vs forever?
  • Who adjusted timing/iterations to balance the game?
  • Note pupils ready to mentor others next session.

← Back to Autumn 2025 Overview