repeat 10run ten waves
Lesson / Scratch & Game Design
How Many Times Should the Snowballs Attack?
One snowball is an inconvenience. Fifty copied snowball scripts are a maintenance problem. Put the attack in a loop, control its timing, and give it a reason to stop.
Lesson plan
Find the repeated work
Mark the snowball actions that would otherwise be copied.
Compare three loops
Try repeat, forever, and repeat-until with short visible examples.
Build the attack
Create the fall-and-reset cycle, then add catches, misses, and waves.
Tune the repetition
Change the delay or stopping condition and test whether the game remains playable.
Explain the loop
Show what repeats, what changes each time, and what makes it stop.
Learning goals
- Spot instructions that repeat.
- Choose between repeat, forever, and repeat-until.
- Count iterations.
- Control the pace of a loop.
- Point to the rule that stops it.
Small examples
foreverkeep checking for the life of the game
repeat until score = 8stop when the goal is reached
wait 0.5 secondsleave time between iterations
Guided project
Attack of the Angry Snowballs
Move the catcher, survive the changing attack patterns, and keep the town's emergency cocoa out of the snow.
A controllable catcher, Repeated falling snowballs, Random starting positions, Collision and missed-object rules.
Loops, Randomness, Coordinates, Collision, Score.
A working version with a tested change, one repaired problem, and a clear explanation.
Teacher checkpoints
- 1Copied blocks have been replaced by a loop.
- 2The student predicts how many times it will run.
- 3Something inside the loop changes each time.
- 4The game has a clear stop or state rule.
- 5The student adjusts the timing independently.
Common mistakes
- Blocks beneath a forever loop never run.
- Nothing inside repeat-until can make its condition true.
- Hazards appear too quickly to play or inspect.
- Starting values are reset during every wave.
Optional challenges
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
- What repeats?
- How many times?
- What changes each time?
- What stops the loop?
- Which repeated copy did you remove?