The Green Flag & Stop Sign — Scratch L1

WHAT IT SHOULD LOOK LIKE

Where this arc is heading: by Lesson 6 your cat and its friend move into position and greet each other on one green-flag click.

both in position

step 1 of 3

the sprites move as they would on the real Stage

Learning Goals 3 min

By the end of this lesson you will be able to:

Point to the green flag and the red stop sign above the Stage.
Explain that when flag clicked waits for the flag, then runs everything below it.
Click the stop sign mid-script and watch a slow stack of moves freeze on the spot.

Warm-Up 7 min

You can find any block now. But every script you have built so far finishes in a blink — too fast to watch, and far too fast to stop. Today you slow the cat down, then learn the button that halts it.

WHAT IT SHOULD LOOK LIKE

Where we are now. Named cat, fixed mark, three-colour stack. The trouble is that it runs so fast there is nothing to watch — and nothing to stop.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Quick-fire puzzle

Wei Jie built this stack and clicked the green flag once. How does the cat behave?


when flag clicked
move (20) steps
move (20) steps
move (20) steps
move (20) steps
move (20) steps

Five move blocks under one hat. One flag click.

Reveal the answer

The cat moved 100 steps in what looked like a single jump. Scratch ran the five blocks top to bottom so quickly that your eye never caught the middle. The cat’s x went 20, 40, 60, 80, 100 — but you only saw the end of it.

Five blocks, no pauses, nothing to see. That is the problem today’s lesson solves.

New Concept — start, slow down, stop 15 min

Think of a school race. The teacher waves a green flag and everyone runs. The teacher blows a whistle and everyone stops. Scratch has exactly those two signals, sitting side by side just above the Stage.

The two buttons

Button	Where	What it does
Green flag	above the Stage, on the right	Starts every script that begins with `when flag clicked`.
Red stop sign	right beside the green flag	Halts every running script at once. Sprites freeze exactly where they are.

The two buttons sit together above the Stage. Green starts every flag script at once; red stops every running script at once.

Hat blocks listen for events

A hat block has a rounded top and can only sit at the very top of a stack. Its only job is to wait for something to happen, then let the blocks underneath run.

when flag clicked waits for the green flag.
Other hats wait for a key press or a sprite click — you meet those in Lessons 16 and 17.
A stack with no hat just sits there. Click the flag and nothing happens: it never got a go signal.

The new block: wait

Here is the block that makes the stop sign worth having. wait (1) seconds lives in the soft-orange Control category. It pauses a script for as long as you tell it, then carries on.

Drop a wait between two moves and the cat stops teleporting — it strolls. And a strolling cat is one you can actually catch with the stop sign.

The number can be a decimal. 0.5 is half a second, 0.1 is a flicker, 3 is a long dramatic pause.

What happens when you click the flag

You click the green flag above the Stage.
Scratch calls out “flag clicked!” to every sprite.
Every when flag clicked hat in the project wakes up.
The blocks under each hat run top to bottom, pausing at each wait.

Why it matters

Your scripts are about to get long — a stroll, a dance, a chase. When something goes wrong, and it will, you need an instant kill switch. That is the stop sign, and knowing it is there makes Scratch safe to experiment in.

Worked Example — build a slow walk, then halt it 15 min

Open your project. Today we build a deliberately slow script, so the stop sign finally has something to interrupt.

WHAT IT SHOULD LOOK LIKE

Stage plan. Four small hops, one second apart. Slow enough that the stop sign can catch the cat between any two of them.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Step 1 — Drag the hat block

From the yellow Events category, drag when flag clicked into the Script Area.

Step 2 — Snap four move blocks underneath

From the blue Motion category, snap four move (10) steps blocks under the hat. Click the flag now — the cat jumps 40 pixels instantly. Blink and you miss it.

Step 3 — Slide a wait between each move

Now the trick. Click the soft orange Control dot and drag wait (1) seconds into the gaps, so the stack alternates: move, wait, move, wait, move, wait, move.


when flag clicked
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps

Eight blocks — right on the Level 1 cap. The cat now hops 10 pixels once a second, four times over.

Step 4 — Click the green flag

Watch the Stage. Hop. Pause. Hop. Pause. Four hops and three waits, about three seconds altogether. Same 40 pixels as before, but now you can actually see it happen.

Step 5 — Run it again, then hit the stop sign

Click the flag, then after the first or second hop click the red octagon. The cat freezes right there. The remaining moves never run at all.

Step 6 — Check where it stopped

Look at the x box in the Sprite Properties bar. If you caught the cat after two hops it reads 20 more than where you started. The stop sign did not rewind anything — it simply stopped time.

What changed: the same four moves that used to be invisible are now a walk you can watch, interrupt, and measure. Adding time to a script is what makes it feel alive.

The full assembled stack (your reference)


when flag clicked
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps

Your finished Worked Example. Green flag starts it; red stop sign halts it wherever you like.

Try It Yourself — three small builds 12 min

🟢 Easy

Goal: Make the cat hop three times, a second apart. Run it once all the way through. Then run it again and stop it after the first hop.

WHAT IT SHOULD LOOK LIKE

Three hops, one second apart. Your second run should freeze the cat after hop 1.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
move (30) steps
wait (1) seconds
move (30) steps
wait (1) seconds
move (30) steps

Think: without the waits, all three moves happen in one instant. The waits are what give your finger a window to land on the stop sign.

🟡 Medium

Goal: Give the walk a rhythm. Make the first pause short and the second one long, so the cat hurries, then dawdles.

WHAT IT SHOULD LOOK LIKE

Same three hops, uneven pauses. Listen to the rhythm rather than watching the distance.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
move (30) steps
wait (0.5) seconds
move (30) steps
wait (2) seconds
move (30) steps

Think: the number inside wait (1) seconds can be a decimal. Try 0.1 for a flicker or 3 for a long dramatic pause. Timing is how animation gets its personality.

🔴 Stretch

Mini-mission: the sniper stop. Wei Jie bets you cannot freeze the cat on an exact spot. Set the cat’s starting x to -100, build a slow shuffle, and try to stop it with x reading exactly -80.

WHAT IT SHOULD LOOK LIKE

Freeze the cat on the red line — not before it, not past it.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

It works if: after you hit the stop sign, the x box reads exactly -80. Write down three attempts and your closest result. Use no more than 8 blocks.


when flag clicked
move (5) steps
wait (1) seconds
move (5) steps
wait (1) seconds
move (5) steps
wait (1) seconds
move (5) steps

Starter stack — a slow shuffle. Change the step size if it makes your target easier to hit.

Think: starting at −100 and needing −80 means 20 pixels of travel. With 5-step hops that is exactly four hops — so the real question is whether you can stop after the fourth and before anything else.

Mini-Challenge — the freeze game 5 min

“Aisyah’s musical statues”

Send the cat on a slow walk across the Stage. A partner shouts “FREEZE!” at a moment of their choosing, and you must halt the cat before its next hop. Where it lands is your score.

WHAT IT SHOULD LOOK LIKE

Goal: the cat walks slowly enough that a shouted FREEZE can actually catch it.

green flag — the cat sets off

step 1 of 2

the sprite moves as it would on the real Stage

It works if:

You use only blocks from today’s lesson and Lesson 1.
The cat moves at least three times when nobody shouts.
The walk is slow enough that a shout gives a real chance to react.
You can show the cat freezing mid-walk on the red stop sign.

Reveal one valid solution (teacher)

One-second waits give a comfortable shouting window; four hops of 20 steps gives four chances.


when flag clicked
move (20) steps
wait (1) seconds
move (20) steps
wait (1) seconds
move (20) steps
wait (1) seconds
move (20) steps

Score by the cat’s final x. Nearer the start means a quick finger; nearer the end means the cat almost got away.

🚀 Mission — Start & Stop, cleanly

WHAT IT SHOULD LOOK LIKE

A scene with a proper beginning and a proper end — and a stop sign that can cut it short at any moment.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Faiz wants to show his little sister a real scene, not a flicker. Build one that starts on the flag, unfolds slowly enough to watch, and finishes with the cat announcing that the show is over.

One flag click runs the whole thing — a single hat block, nothing else to press.
The cat must move more than once, with enough of a pause that his sister can follow it.
The cat ends by saying a closing line you wrote yourself.
The stop sign must be able to cut the scene short at any moment, cleanly.
Use no more than 8 blocks.

✅ Done when: the scene is watchable from start to finish, ends with the cat’s line, and freezes instantly whenever you hit the stop sign. Going further: make the pauses uneven so the walk has a rhythm.

Teacher notes — one setup that satisfies the brief

Seven blocks: when flag clicked, then move (30) steps / wait (1) seconds twice, then say [Scene done!] for (2) seconds. Pupils who put the say block before the moves have still met the brief only if the cat announces the end — worth a discussion about ordering.

Recap 2 min

Today you met the two buttons above the Stage. The green flag starts every script that begins with when flag clicked; the red stop sign halts everything at once. You also met wait (1) seconds, the small Control block that turns an invisible teleport into a walk you can watch.

Green flag: The button above the Stage that starts every script beginning with a flag hat block.
Stop sign: The red octagon beside the flag. One click halts every running script at once.
Hat block: A block with a rounded top that sits at the top of a script and waits for an event.
wait (block): A Control block that pauses a script for a number of seconds — decimals allowed.

Homework 1 min

Catch the Cat. Walk the cat in from the left edge and try to freeze it exactly on the centre spot. Three attempts, and write down how close you got each time.

WHAT IT SHOULD LOOK LIKE

Start on the left, hop toward the middle, and hit the stop sign the instant the cat lands in the ring.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Set the cat’s x to -200 in the Sprite Properties bar.
Build the stack below — three hops with a second between each.
Click the flag, then hit the stop sign as near to x = 0 as you can manage.
Read the x box and write the number down. Reset to -200 and try twice more.


when flag clicked
move (40) steps
wait (1) seconds
move (40) steps
wait (1) seconds
move (40) steps

Your homework stack — seven blocks, three hops, two pauses.

Bring back next class:

A screenshot of your Script Area showing the seven-block stack.
Your three attempts written out: “Attempt 1: x = ___. Attempt 2: x = ___. Attempt 3: x = ___. Closest to 0 was ___.”

Heads up for next class: SCR-L01-05 shows you how to add a second sprite from the library — the cat is about to get company.

WHAT IT SHOULD LOOK LIKE

Where this arc is heading: by Lesson 6 your cat and its friend move into position and greet each other on one green-flag click.

both in position

step 1 of 3

the sprites move as they would on the real Stage

Learning Goals 3 min

By the end of this lesson you will be able to:

Point to the green flag and the red stop sign above the Stage.
Explain that when flag clicked waits for the flag, then runs everything below it.
Click the stop sign mid-script and watch a slow stack of moves freeze on the spot.

Warm-Up 7 min

WHAT IT SHOULD LOOK LIKE

Where we are now. Named cat, fixed mark, three-colour stack. The trouble is that it runs so fast there is nothing to watch — and nothing to stop.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Quick-fire puzzle

Wei Jie built this stack and clicked the green flag once. How does the cat behave?


when flag clicked
move (20) steps
move (20) steps
move (20) steps
move (20) steps
move (20) steps

Five move blocks under one hat. One flag click.

Reveal the answer

Five blocks, no pauses, nothing to see. That is the problem today’s lesson solves.

New Concept — start, slow down, stop 15 min

The two buttons

Button	Where	What it does
Green flag	above the Stage, on the right	Starts every script that begins with `when flag clicked`.
Red stop sign	right beside the green flag	Halts every running script at once. Sprites freeze exactly where they are.

The two buttons sit together above the Stage. Green starts every flag script at once; red stops every running script at once.

Hat blocks listen for events

A hat block has a rounded top and can only sit at the very top of a stack. Its only job is to wait for something to happen, then let the blocks underneath run.

when flag clicked waits for the green flag.
Other hats wait for a key press or a sprite click — you meet those in Lessons 16 and 17.
A stack with no hat just sits there. Click the flag and nothing happens: it never got a go signal.

The new block: wait

Here is the block that makes the stop sign worth having. wait (1) seconds lives in the soft-orange Control category. It pauses a script for as long as you tell it, then carries on.

Drop a wait between two moves and the cat stops teleporting — it strolls. And a strolling cat is one you can actually catch with the stop sign.

The number can be a decimal. 0.5 is half a second, 0.1 is a flicker, 3 is a long dramatic pause.

What happens when you click the flag

You click the green flag above the Stage.
Scratch calls out “flag clicked!” to every sprite.
Every when flag clicked hat in the project wakes up.
The blocks under each hat run top to bottom, pausing at each wait.

Why it matters

Worked Example — build a slow walk, then halt it 15 min

Open your project. Today we build a deliberately slow script, so the stop sign finally has something to interrupt.

WHAT IT SHOULD LOOK LIKE

Stage plan. Four small hops, one second apart. Slow enough that the stop sign can catch the cat between any two of them.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Step 1 — Drag the hat block

From the yellow Events category, drag when flag clicked into the Script Area.

Step 2 — Snap four move blocks underneath

From the blue Motion category, snap four move (10) steps blocks under the hat. Click the flag now — the cat jumps 40 pixels instantly. Blink and you miss it.

Step 3 — Slide a wait between each move

Now the trick. Click the soft orange Control dot and drag wait (1) seconds into the gaps, so the stack alternates: move, wait, move, wait, move, wait, move.


when flag clicked
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps

Eight blocks — right on the Level 1 cap. The cat now hops 10 pixels once a second, four times over.

Step 4 — Click the green flag

Watch the Stage. Hop. Pause. Hop. Pause. Four hops and three waits, about three seconds altogether. Same 40 pixels as before, but now you can actually see it happen.

Step 5 — Run it again, then hit the stop sign

Click the flag, then after the first or second hop click the red octagon. The cat freezes right there. The remaining moves never run at all.

Step 6 — Check where it stopped

Look at the x box in the Sprite Properties bar. If you caught the cat after two hops it reads 20 more than where you started. The stop sign did not rewind anything — it simply stopped time.

What changed: the same four moves that used to be invisible are now a walk you can watch, interrupt, and measure. Adding time to a script is what makes it feel alive.

The full assembled stack (your reference)


when flag clicked
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps
wait (1) seconds
move (10) steps

Your finished Worked Example. Green flag starts it; red stop sign halts it wherever you like.

Try It Yourself — three small builds 12 min

🟢 Easy

Goal: Make the cat hop three times, a second apart. Run it once all the way through. Then run it again and stop it after the first hop.

WHAT IT SHOULD LOOK LIKE

Three hops, one second apart. Your second run should freeze the cat after hop 1.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
move (30) steps
wait (1) seconds
move (30) steps
wait (1) seconds
move (30) steps

Think: without the waits, all three moves happen in one instant. The waits are what give your finger a window to land on the stop sign.

🟡 Medium

Goal: Give the walk a rhythm. Make the first pause short and the second one long, so the cat hurries, then dawdles.

WHAT IT SHOULD LOOK LIKE

Same three hops, uneven pauses. Listen to the rhythm rather than watching the distance.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
move (30) steps
wait (0.5) seconds
move (30) steps
wait (2) seconds
move (30) steps

Think: the number inside wait (1) seconds can be a decimal. Try 0.1 for a flicker or 3 for a long dramatic pause. Timing is how animation gets its personality.

🔴 Stretch

WHAT IT SHOULD LOOK LIKE

Freeze the cat on the red line — not before it, not past it.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

It works if: after you hit the stop sign, the x box reads exactly -80. Write down three attempts and your closest result. Use no more than 8 blocks.


when flag clicked
move (5) steps
wait (1) seconds
move (5) steps
wait (1) seconds
move (5) steps
wait (1) seconds
move (5) steps

Starter stack — a slow shuffle. Change the step size if it makes your target easier to hit.

Mini-Challenge — the freeze game 5 min

“Aisyah’s musical statues”

Send the cat on a slow walk across the Stage. A partner shouts “FREEZE!” at a moment of their choosing, and you must halt the cat before its next hop. Where it lands is your score.

WHAT IT SHOULD LOOK LIKE

Goal: the cat walks slowly enough that a shouted FREEZE can actually catch it.

green flag — the cat sets off

step 1 of 2

the sprite moves as it would on the real Stage

It works if:

You use only blocks from today’s lesson and Lesson 1.
The cat moves at least three times when nobody shouts.
The walk is slow enough that a shout gives a real chance to react.
You can show the cat freezing mid-walk on the red stop sign.

Reveal one valid solution (teacher)

One-second waits give a comfortable shouting window; four hops of 20 steps gives four chances.


when flag clicked
move (20) steps
wait (1) seconds
move (20) steps
wait (1) seconds
move (20) steps
wait (1) seconds
move (20) steps

Score by the cat’s final x. Nearer the start means a quick finger; nearer the end means the cat almost got away.

🚀 Mission — Start & Stop, cleanly

WHAT IT SHOULD LOOK LIKE

A scene with a proper beginning and a proper end — and a stop sign that can cut it short at any moment.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Faiz wants to show his little sister a real scene, not a flicker. Build one that starts on the flag, unfolds slowly enough to watch, and finishes with the cat announcing that the show is over.

One flag click runs the whole thing — a single hat block, nothing else to press.
The cat must move more than once, with enough of a pause that his sister can follow it.
The cat ends by saying a closing line you wrote yourself.
The stop sign must be able to cut the scene short at any moment, cleanly.
Use no more than 8 blocks.

Teacher notes — one setup that satisfies the brief

Recap 2 min

Green flag: The button above the Stage that starts every script beginning with a flag hat block.
Stop sign: The red octagon beside the flag. One click halts every running script at once.
Hat block: A block with a rounded top that sits at the top of a script and waits for an event.
wait (block): A Control block that pauses a script for a number of seconds — decimals allowed.

Homework 1 min

Catch the Cat. Walk the cat in from the left edge and try to freeze it exactly on the centre spot. Three attempts, and write down how close you got each time.

WHAT IT SHOULD LOOK LIKE

Start on the left, hop toward the middle, and hit the stop sign the instant the cat lands in the ring.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Set the cat’s x to -200 in the Sprite Properties bar.
Build the stack below — three hops with a second between each.
Click the flag, then hit the stop sign as near to x = 0 as you can manage.
Read the x box and write the number down. Reset to -200 and try twice more.


when flag clicked
move (40) steps
wait (1) seconds
move (40) steps
wait (1) seconds
move (40) steps

Your homework stack — seven blocks, three hops, two pauses.

Bring back next class:

A screenshot of your Script Area showing the seven-block stack.
Your three attempts written out: “Attempt 1: x = ___. Attempt 2: x = ___. Attempt 3: x = ___. Closest to 0 was ___.”

Heads up for next class: SCR-L01-05 shows you how to add a second sprite from the library — the cat is about to get company.