repeat 10run a known number of waves
Public lesson / Scratch & Game Design
How Many Times Should the Snowballs Attack?
A snowball attack works once. Copying it fifty times works too, but nobody wants to repair fifty copies when the timing changes. What should repeat, and what should stop it?
Lesson rhythm
The idea moves toward a demonstration.
Story, problem, or provocation
Name the problem before opening the build.
Theory and concept
Make the hidden rule visible with small tests.
Guided build
Use the idea inside a working project system.
Modification challenge
Change one rule and predict the effect.
Demonstration and cleanup
Explain the result, save safely, and leave a known state.
Learning goals
What students should be able to do and explain.
- Recognize repeated instructions.
- Choose repeat, forever, or repeat-until.
- Count iterations.
- Change timing inside a loop.
- Explain a stop condition.
Theory kernel
Small examples before the larger build.
foreverkeep checking while the game runs
repeat until score = 8stop after a goal
wait 0.5 secondsmake repetition observable
Guided-build preview
Attack of the Angry Snowballs
Keep the town's emergency mug of cocoa safe while angry snowballs fall in patterns that become faster and harder to predict.
A controllable catcher, Repeated falling snowballs, Random starting positions, Collision and missed-object rules.
Loops, Randomness, Coordinates, Collision, Score.
A working version, one modification, one repaired problem, and an explanation.
Teacher checkpoints
Evidence before adding complexity.
- 1Student replaces copied blocks with a loop.
- 2Student predicts the repeat count.
- 3The loop contains a changing action.
- 4The game has a stop or state rule.
- 5Student tunes timing independently.
Common mistakes
Pause, inspect, and test one cause.
- A forever loop blocks later code.
- Repeat-until never changes its condition.
- The loop creates objects too quickly.
- Setup accidentally repeats with every wave.
Modification challenge
Three levels, one concept kept visible.
Higher levels are optional. They deepen the current idea rather than turning a beginner lesson into an unrelated advanced task.
Builder
- Add a fixed second wave.
Inventor
- Shorten the delay as score rises.
Boss Level
- Create wave states with different patterns.
End-of-class demonstration
Explain the work while it is still visible.
- What repeats?
- How many times?
- What changes each time?
- What stops the loop?
- Which repeated copy did you remove?