Chapter 5

Mental models

Mental models are thinking shortcuts that work almost anywhere: at school, at home, and in games.

8 activities inside

Before you start: Remember a time you flipped a problem around to solve it, or thought a few steps ahead. Tell a grown-up about it.

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models · Inversion 15 min · pencil ★☆☆

The worst birthday party ever

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Inversion means flipping a problem upside down. To plan the best party, first plan the worst!

List ways to make a party terrible.
Flip each one into a way to make it great.

Example: Worst: invite nobody. Flip it: send invites a week early.

How to make it the WORST	Flip it: how to make it the BEST

Grown-up corner

Why it matters: Thinking about how things could go wrong helps us avoid mistakes. Pilots and doctors use this too.

Which “worst” idea was the funniest?
Which flipped idea will you really use?

Extend it: Use inversion on a school morning: what makes it the worst? Then flip it.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · Second-order thinking 15 min · pencil ★★☆

And then what?

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Second-order thinking means asking “and then what?” again and again.

Ask “and then what?” and write what happens next.
Keep going. Is the last box good or bad?

Example: It rains all week → the plants grow → more bugs → more birds visit.

Ice cream is free at school every day!

And then what?

Grown-up corner

Why it matters: The first result of a choice is easy to see. Good thinkers also look at what comes after.

Was the last box good or bad?
Who else is affected further down the chain?

Extend it: Ask “and then what?” about a real family decision.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · First principles 20 min · pencil ★★★

What is a chair really for?

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First principles means asking what something is really for, then building from there.

List the jobs a chair really does (not what it looks like).
Forget every chair you have seen.
Draw something new that does those jobs.

Example: Jobs: hold me up, rest my back, keep me off the floor…

Jobs a chair does

My new design

Grown-up corner

Why it matters: Inventors break ideas down to basic truths, then rebuild. It frees kids from “that’s how it’s always done”.

Which job is the most important?
Could your design do a job a chair can’t?

Extend it: Try it with a backpack or a toothbrush.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · Opportunity cost 15 min · pencil, scissors ★★☆

One free hour

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You have one free hour (60 minutes). Every choice means giving something else up.

Cut out the cards.
Pick cards that add up to 60 minutes or less. Write their letters in the boxes.
Look at what you gave up. That is your opportunity cost!

I choose (60 min)Card letters:

I give upCard letters:

APlay football: 30 min

BRead a comic: 20 min

CBake with a grown-up: 40 min

DCall a cousin: 10 min

EDraw: 20 min

FVideo game: 30 min

GBuild a fort: 40 min

HHelp a neighbor: 20 min

Grown-up corner

Why it matters: Every yes is also a no to something else. Seeing that helps kids make choices on purpose.

Which card was hardest to give up?
Would you choose differently on a rainy day?

Extend it: Do the same with pocket money: what does buying one thing cost you?

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · Compounding 15 min · pencil, calculator (optional) ★★☆

Rice on a chessboard

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A clever girl asks the king for rice: 1 grain on day 1, then double each day. The king laughs. Should he?

Day 1 is 1 grain. Day 2 is 2. Keep doubling.
Fill in all 16 days.
Guess: how much on day 64?

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Day 7

Day 8

Day 9

Day 10

Day 11

Day 12

Day 13

Day 14

Day 15

Day 16

My guess for day 64:

Grown-up corner

Why it matters: Compounding means growth on top of growth. Small steady gains, in money or skills, get huge over time.

When did the numbers start to feel big?
What else grows like this? (Reading, practice, savings.)

Extend it: Read 5 more minutes each week and track how your total grows.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · Base rates 15 min · pencil ★★☆

Guess the left-handers

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A base rate is how common something usually is. It helps you make smarter guesses.

Write a quick guess.
Use the base rate to make a better guess.
Ask 30 people (a class, a team or your family and friends). Count the left-handers.

Question: Predict for a class of 30 kids: how many are left-handed?

My quick guess (out of 30):

Base rate: about 1 in 10 people are left-handed. So in 30 kids, about:

I asked 30 people. Left-handed:

Was my first guess or my base-rate guess closer to what I found?

Grown-up corner

Why it matters: People often guess from a story they remember instead of how common things really are. Base rates fix that.

Why might your own class be different?
What else could you guess with a base rate?

Extend it: Guess how many red cars you will see on a drive, then count.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · Map vs territory 20 min · pencil, a colored pencil ★★☆

Draw your street from memory, then check

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A map is never the real place. It always leaves things out. Let’s see what yours misses!

Draw your street from memory in the first box.
Walk it with a grown-up. In the second box, draw or list what you missed.
Circle the thing that surprised you most.

My street from memory

What I missed

Grown-up corner

Why it matters: Our picture in our heads is like a map: useful, but not the real thing. Checking helps kids update their ideas.

Why did you remember some things and not others?
What would a map for a cat need to show?

Extend it: Optional: compare your map with an online map of your street.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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models · Incentives 15 min · pencil ★★★

Why are sweets at the checkout?

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An incentive is a reward that makes people act a certain way. Shops, games and rules all use them.

Answer the shop question.
Make a chore rule.
Find the cheat, then fix it!

Why do shops put sweets near the checkout?

My chore rule (with a reward):

How someone could cheat it:

My cheat-proof rule:

Grown-up corner

Why it matters: Spotting incentives helps kids understand why people and shops behave as they do, and design fairer rules.

Who wins when sweets are at the checkout?
Did your cheat-proof rule really stop cheating?

Extend it: Spot 3 incentives next time you go shopping together.

My brain felt: ☐ easy ☐ just right ☐ stretchy

One thing I learned: ________________________

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