Scratch: Space Game with Cloning

Board‑ready tiles • simple flow • identity focus: everyone here is a coder.
Jump to Steps

Teaching Pedagogy

Lesson objectives

What we are learning

  • Create clones to spawn repeated asteroids.
  • Position sprites with go to x/y; move with change x by.
  • Control with repeat until using x position < −240.
  • Explain how cloning saves time vs. many sprites.
Success criteria

What great looks like

  • Asteroids appear continuously at random heights.
  • They move left and delete when off‑screen.
  • You can describe the clone pattern from memory.
Vocabulary

Words coders use

  • Sprite — object/character.
  • Script — stack of blocks.
  • Clone — fast copy made by code.
  • Event — start signal (green flag).
  • Loop — do it again and again.
  • Condition — test, e.g. x position < −240.
Teacher moves

Running the room

  • Pairs share one keyboard; swap driver every 5 minutes.
  • One student volunteer models actions while the class builds along.
  • Use “small steps → test”: press the flag after each block stack.
Typical questions

Check understanding

  • Where do clones start and why use pick random for y?
  • What happens if wait = 0.2 or 1.2?
  • What breaks without delete this clone?
  • Why not touching edge? here?
What it’s like to be a coder

Coder mindset

  • Talk in blocks: “Events → flag; Control → repeat until …”.
  • Read clues: nothing shows → check show/green flag.
  • Debug calmly: change one thing, test, repeat.

Step‑by‑Step Guide

Colour‑matched to Scratch
1Delete the cat → choose a rock → rename to Asteroid.
2Events when green flag clicked → Looks hide
3New script: Events when green flag clicked → Control forever → inside add create clone of myself then wait 0.7 seconds.
4New script: Control when I start as a clone → Motion go to x: 240 y: pick random −170 to 170 → Looks show.
5Control repeat until (x position < −240) → inside add Motion change x by −10 → after loop add Control delete this clone.

Why not touching edge? Starting at x=240 often counts as “touching” and skips movement. The x position test waits until the clone moves off‑screen.

Visual reference

Blocks at a glance

Scratch blocks: hide on green flag; spawner with create clone and wait; clone script with go to x 240, random y, show, repeat until x position < -240, change x by -10, delete this clone

Troubleshoot & Extend

Fast fixes
  • See nothing? Add show in the clone script and press the flag.
  • Clones vanish? Use x position < −240 (not touching edge?).
  • Laggy? Add delete this clone after the loop.
  • Same height? Put pick random −170 to 170 in the y slot.
Wow moments

For early finishers

  • Add a Score variable and +1 when a laser hits an asteroid.
  • Increase speed every 10 points (use a speed variable).
  • Change costume each spawn for visual variety.
  • Add a Lives variable and end the game when it reaches 0.

Tip: project in Presenter Mode for bigger text. This layout keeps the pedagogy up top and the step‑by‑step with a visual reference just below.