From Scratch Programming Class

Session 7: Putting it together — a small game

Phase 1 — Scratch · Session 7 of 9

What we’re learning today

You’ve now learned every basic idea you need to build games: sequences, loops, events, conditionals, sensing, and variables. Today we’ll combine all of them into one small game called Apples and Rocks — catch the falling apples for points, but dodge the falling rocks or it’s game over. By the end, you’ll have a complete, playable game with a score and a real losing condition.

You’ll need to remember from last time

• Variables — set, change, (read), displayed on stage.
• The if block + sensing for collision detection.
• Forever loops for things that keep happening.
• Events for arrow-key control.
• Multiple sprites with their own scripts.

That’s basically the whole curriculum so far. Today is the test: can you put it all together?

Part A: Build the basic game (apples falling, score going up)

Open Scratch and start a new project. (Don’t open last week’s — we’ll build the whole game from scratch so you remember every piece.)

This first half is essentially the catch-the-apple game from Sessions 5 and 6, rebuilt cleanly in one go. If you’ve kept up, this should feel like review. That’s the point — you’re proving to yourself that you can build this from memory.

Anatomy of this game (how the parts fit together)

Before you start clicking blocks, look at the shape of what you’re building. Three sprites, each with its own job:

Cat sprite (the player)
  on green flag:
    [reset position, reset score]
    forever:
      [if right arrow → move right]
      [if left arrow → move left]

Apple sprite (the good thing)
  on green flag:
    [start at top, random x]
    forever:
      [fall down]
      [if touching cat → +1 score, restart at top]
      [if off bottom → restart at top]

Rock sprite (the bad thing) — added in Part B
  on green flag:
    [start at top, random x]
    forever:
      [fall down]
      [if touching cat → say "Game Over!", stop everything]
      [if off bottom → restart at top]

Each sprite is a tiny machine that runs forever once you press the green flag. They don’t know about each other except through touching checks. Keep this map in your head as you build.

Set up the cat

Build this on the cat:

when [green flag] clicked
go to x: 0 y: -130
set [score] to 0
forever
   if <key [right arrow] pressed?> then
      change x by 7
   if <key [left arrow] pressed?> then
      change x by -7

(Make a score variable first if you haven’t — Variables category → Make a Variable → name it score → OK.)

The cat sits at the bottom of the stage and slides left/right with the arrow keys. Score resets to 0 on green flag.

Add the apple

Click Choose a Sprite (bottom right). Search for “apple” and add one (or any small fruit/food sprite).

Switch to the apple’s scripts (click the apple in the sprite list). Build:

when [green flag] clicked
go to x: pick random -200 to 200 y: 180
forever
   change y by -3
   if <touching [Sprite1] ?> then
      change [score] by 1
      go to x: pick random -200 to 200 y: 180
   if <(y position) < -180> then
      go to x: pick random -200 to 200 y: 180

(Replace Sprite1 with whatever your cat is named in the dropdown. Often it’s Cat or Sprite1.)

The apple falls, gives you a point if the cat catches it, resets to the top either way (catch or miss).

Click the green flag. Move the cat. Catch some apples. Watch the score go up.

This is the base game — same as before, just rebuilt cleanly.

Checkpoint: You have a working catch-the-apple game with a visible score that increases when the cat catches apples. This is the natural stop point if class is cut short — Part B adds the hazard mechanic but isn’t required.

Part B: Add the rock (game over!)

Now we’ll make this a real game by adding risk. Right now you can just stand still and you don’t lose anything. Boring. Time to add a falling rock that ends the game if you touch it.

Add the rock sprite

Click Choose a Sprite again. Search for “rock” — there’s a Rocks sprite in the library. (Or pick anything that looks like something you wouldn’t want to touch — a bug, a skull, a “Block.”)

Switch to the rock’s scripts. Build:

when [green flag] clicked
go to x: pick random -200 to 200 y: 180
forever
   change y by -3
   if <touching [Sprite1] ?> then
      say [Game Over!] for 2 seconds
      stop [all]
   if <(y position) < -180> then
      go to x: pick random -200 to 200 y: 180

The rock falls just like the apple, but:

• If it touches the cat: say “Game Over!” for 2 seconds, then stop [all] (Control category) — this freezes the entire program.
• If it falls off the bottom: reset to top with new random x. (No penalty for letting a rock pass — that’s actually what you want to happen.)

Click the green flag. Move the cat. Catch apples. Dodge the rock.

When the rock catches you, the cat says “Game Over!” and everything freezes. Your final score sits on the screen as your record.

You just built a game with a real losing condition. Welcome to actual game design.

That’s the base goal for today. If your apples-and-rocks game runs and ends correctly, you’re done.

Stretch goal

Right now the apple and the rock fall at the same speed. Make the rock slightly faster than the apple to ramp up the challenge:

In the rock’s forever loop, change change y by -3 to change y by -4 or -5. Now the rock is harder to dodge.

Then make a second apple sprite (right-click the apple in the sprite list → duplicate). Two apples falling at once means more points but also more places to be at the wrong moment.

Extension

Add a “best” score variable that survives across plays in the same session. Add to the cat’s scripts:

when [space] key pressed
if <(score) > (best)> then
   set [best] to (score)

(You’ll need to make a best variable first.)

Now: when you press space at the end of a game (after game over), your score gets compared to best, and best updates if you beat it. Across multiple games, you can keep trying to beat your own record. Press the green flag to start over each time.

For an even bigger challenge: what if score went DOWN by 1 each time the apple falls without being caught? Add change [score] by -1 inside the apple’s (y position) < -180 block. Now you can have a negative score, and missing apples is genuinely costly.

Wrap-up

Before we leave, a few things to share:

• What was the highest score anyone got before the rock caught them?
• Did the rock-faster-than-apple stretch make the game feel meaningfully different?
• For the kids who did the “best” extension — does adding a high score change how you play?
• Did anything break in surprising ways while you were building it? This is the most important question. Programmers spend most of their time fixing things that broke. Your stories matter.

You did something today that you couldn’t have done six weeks ago. You took a blank Scratch project and built a complete game that has a goal, a challenge, scoring, and a way to lose. Every video game you’ve ever played has those four things. You now know how to put them in something you built.

Looking ahead to your own project

Next week we start your milestone project — your game, your idea, your design. You’ll have two weeks to plan, build, and polish, then you’ll show it to the class.

Start thinking now: what do you want to make? Some ideas to get you started:

• A different kind of catch game (catching different things, different objectives)
• A maze game where the cat has to reach a goal without touching the walls
• A drawing toy (using the pen extension from Session 3)
• A mini-quiz where the cat asks questions and reacts to clicks
• A “boss battle” where you click a sprite many times to defeat it
• An interactive story — multiple sprites, multiple scenes, the user clicks to advance
• Anything else you can imagine that uses what you’ve learned

You don’t have to decide today. But come to next week’s class with at least one idea you’re excited about.

If you missed this session

Open Scratch and start a new project. Then:

1. Build the cat with smooth left/right movement at the bottom of the stage. Reset score to 0 on green flag. (Part A above.)
2. Add an apple that falls, gives a point on catch, resets either way.
3. Add a rock that falls. If it touches the cat: say "Game Over" for 2 seconds, then stop [all]. If it falls off the bottom: reset to top.
4. Test it. Catch apples. Try to dodge the rock.

About 30-40 minutes of work.

Then think about what you want to build for your own project next week. Bring an idea.

If you get stuck, ask your buddy at the start of next class.

Stretch and extension ideas

• Add a backdrop (bottom-right Choose a Backdrop button) so the game has a setting — a forest, a city, outer space.
• Add a sound effect when the cat catches an apple. (Sound category, start sound. Some apple sprites come with sound effects built in.)
• Make the cat change costume when game over fires (look at the Costumes tab — many cats have multiple costumes).
• Add a third “good” sprite (a star, a heart) worth more points than the apple. Now you have to choose what to chase.

What’s next

Next week is the start of your milestone project — two weeks to plan, build, and polish your own game. Bring an idea or two. The final week will be a class demo day where everyone shows what they built.