6th Grade · Ages 11–12
The Doubt Year
Eleven is the year to find out that your gut is confidently, repeatably wrong — and that thirty tally marks settle an argument faster than an hour of shouting.
- 1 Hard Thing
- 5 days · 105 minutes
- 3 unmarkable questions
The Hard Thing · about a grade above
Three Doors
A prize sits behind one of three doors. You pick door 1. The host, who knows where the prize is, opens door 3 and shows you it is empty. He offers you the swap to door 2. Do you swap — and does it even matter?
Stuck for ten minutes? Good. Open one hint, not three.
1Hint 1
Your first pick was right 1 time in 3. Opening a door afterwards does not travel back in time and change that.
2Hint 2
The host is not choosing at random. He will never open the prize door. That single fact is the whole puzzle.
3Hint 3
Stop arguing. Play it thirty times with three cups and a coin, and write the score down.
The answer — only after you have written something down
Swap. Your first door wins one third of the time. The other two doors together hold the prize two thirds of the time — and the host has just squeezed both of those into one door. Swapping wins twice as often. Thirty played rounds will convince a person the argument cannot.
The genius move
“Ask who knew what. A choice made by somebody with information is not a coin flip.”
Five days, five muscles
The week
Never the same muscle two days running. The weekend is not on this list on purpose — being bored is the sixth muscle and it needs two clear days.
- MondayThe Hard Thing
Three Doors. Write down your answer before you reason about it.
25 min - TuesdayBuild
Run thirty rounds with a partner. Tally sheet, two columns: swapped and won, stayed and won.
25 min - WednesdayRead up
Find an argument online where two people are certain of opposite things. Work out what evidence would actually settle it.
20 min - ThursdayTeach
Teach it to an adult. Most adults get it wrong, and watching that happen is the lesson.
15 min - FridayBreak
What if the host opened a door at random and it happened to be empty? Does the answer change? It does — find out why.
20 min
Start Monday now
Read the problem once more, out loud, and press start. Solving it is not the measurement.
Nothing rung today yet
The twenty-five minutes
Four phases. The middle one is most of it, and it is meant to feel slow.
- 1SitRead the problem again, out loud. Write nothing yet.
- 2AttackTry the wrong thing. It is faster than thinking about the right one.
- 3StuckWrite down the exact place you are stuck. “I don’t get it” is not a place.
- 4LogOne sentence: what you will try tomorrow. Then close the book.
No answer key
Three questions you cannot mark
Ask one at dinner. Do not resolve it. A question that survives the washing-up is doing its job.
- ?1
Why is our gut so bad at chance?
- ?2
How many times do you have to see something before you believe it?
- ?3
Can a thing be true when everybody disagrees with you?
Where this goes
The ladder
The same idea, three times, roughly a year apart. This is what depth looks like from the outside.
This year
Three doors, played thirty times.
Next year
A hundred doors, where the host opens ninety-eight. The same puzzle with the fog removed.
The year after
Conditional probability — the grown-up name for who knew what, and when.
What lives on the desk this year
- Three cups and something worth hiding
- A tally sheet
- A partner who will argue with you
- A notebook for predictions written before the result
- One rule: the guess goes down on paper first
The rest of 6th Grade
One hard thing a day is the sharp end. It sits on top of an ordinary year.
Last updated: September 2026