What students build
- A controllable catcher
- Repeated falling snowballs
- Random starting positions
- Collision and missed-object rules
- Score and loss state
- Reliable restart
Guided Class Project
Guided Class ProjectAttack 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.
Visible system / hidden curriculum
Build something clear enough to test.
What students learn
- Choosing a loop
- Random x positions
- Changing y over time
- Collision checks
- Variables and difficulty
- Testing repeated events
What students need
- Browser
- Scratch editor
- Keyboard
- Student-drawn or ordinary built-in assets
No special account or downloaded asset is assumed. Saving and sharing depend on the classroom setup.
Suggested build order
Decisions and checkpoints, not a wall of copied blocks.
Students may use different artwork and implementation details. The shared structure keeps the concept teachable.
- 01
Create the catcher
Task: Place a player-controlled object near the bottom of the stage.
Build and test this part before adding the next system.
- Checkpoint
- Left and right controls stay on screen.
- Likely mistake
- Changing y instead of x.
- 02
Make one snowball fall
Task: Reset one object above the stage and change its y position repeatedly.
Build and test this part before adding the next system.
- Checkpoint
- The snowball crosses the stage visibly.
- Likely mistake
- Moving once instead of inside a loop.
- 03
Randomize the next attack
Task: Choose a new x position before each fall.
Build and test this part before adding the next system.
- Checkpoint
- Several runs begin in different places.
- Likely mistake
- Randomizing during every movement step.
- 04
Detect catch and miss
Task: Use separate rules for touching the catcher and passing the bottom boundary.
Build and test this part before adding the next system.
- Checkpoint
- Each outcome changes state once.
- Likely mistake
- Scoring repeatedly during one contact.
- 05
Build waves
Task: Repeat the fall-reset cycle and change timing after a chosen score.
Build and test this part before adding the next system.
- Checkpoint
- Difficulty changes for an explainable reason.
- Likely mistake
- Creating objects too fast to test.
- 06
Reset the storm
Task: Restore score, timing, positions, and game state.
Build and test this part before adding the next system.
- Checkpoint
- Three restarts behave the same way.
- Likely mistake
- Resetting the score but not the speed.
Test it
Try the edges, not only the easy success.
- Can every snowball be caught?
- Does a miss count once?
- Can a snowball appear outside the playable area?
- Does speed change at the intended score?
- Does restart restore the first-wave timing?
Common mistakes
Read the clues before changing code.
- Random x changes during the fall.
- The miss line is outside the stage.
- Catch and miss happen in the same frame.
- A forever loop prevents the loss screen.
Improve it
Preserve the core system while changing the project.
- Add a rare giant snowball.
- Create two wave patterns.
- Add a temporary shield.
- Make wind change horizontal movement.
Challenge levels
Choose meaningful difficulty.
Builder
Add a survival timer.
Inventor
Create a readable wave system with changing delays.
Boss Level
Design three attack patterns and select them from game state.
Show-teacher checkpoint
Demonstrate the working decisions.
- Working catcher movement
- A repeated attack
- Catch and miss outcomes
- A visible score
- One difficulty change
- One repaired loop bug