Classroom · Game Theory
Twenty coins, one offer, and a room that pays to say no.
One student divides twenty coins; another takes the split or refuses it — and refusing leaves both with nothing. Three rounds against three strangers, with every offer, every refusal and every coin destroyed on the projector.
- In pairs
- About 45 min
- 3 acts
A practice run with fictional students. No real classroom or join code is created.
Try an answer on the phone. Lead the lesson from the screen.
On their phone
You are presenting
Setting up the room…
Lesson deck
Teach it as a ready-made lesson
Hook, how it works, the live game and takeaways. Edit anything.
Take it or leave it
A ready-to-teach lesson deck: a hook, how it works, the live game and takeaways for the debrief.
6 slides · 1 activity
What it teaches
The standard theory says a responder should accept any offer above zero, because something beats nothing. Rooms do not play that way, and the point of running it live is that YOUR room will not either: students discover fairness norms by enforcing them at their own expense, and the board prices exactly what that enforcement cost — the coins the room burned to punish splits it found insulting.
- Fairness norms
- Costly punishment
Debrief, while the boards are still up
- 01
What was the smallest offer that survived — and why did smaller ones die?
- 02
Refusing cost you real coins. What were you buying?
- 03
Would the offers have changed if you played the same person three times instead of three strangers?
How it works
- 01
Add it to your library
Sign up free and pull the activity from Decka's built-in classroom catalog — one click copies it into your own library, ready to run from Decka or inside PowerPoint.
- 02
Students join by QR
Everyone scans from the projector and plays in their phone's browser. No app, no account, nothing to install.
- 03
You run the room
You move the activity phase by phase: collection closes, the boards resolve on the big screen, and the debrief happens while the results are still up.
What is the ultimatum game?
The ultimatum game is the cleanest experiment behavioural economics has: one player proposes a division of a fixed pot, the other accepts it or vetoes it, and a veto destroys the pot for both. If people were the payoff-maximisers of the textbook, proposers would offer almost nothing and responders would take it. Four decades of running the game — in labs, across cultures, at every stake anyone could afford — say otherwise: low offers get refused, routinely, by people who know exactly what refusing costs them.
Played live, that finding stops being a citation. Each round pairs every student with someone they have not played, so a refusal cannot be an investment in a relationship — it is pure, priced punishment. The projector shows every offer the room made, which ones died, and the running total of coins destroyed to say no. That last number is the debrief: the room sits there looking at value it burned voluntarily, and has to explain itself.
FAQ
Ultimatum game questions, answered
Why do students play strangers each round?
The pairing rotates every round so nobody faces the same partner twice. Against a repeated partner, refusing a low offer is an investment — you are training them for next time. Against a stranger it is pure punishment, which is the clean version of the finding the game exists to show.
Are the offers anonymous?
Choices happen on each student's own phone and the projector shows the room's offers and refusals as a distribution, not a name-by-name list — so students respond to the numbers, not to who made them.
How long does it take?
Three short rounds; the default timing ships with the activity and shows under the headline as "About N min". Every duration is adjustable before you run it.
Do students need an app or an account?
No. Students scan a QR code from the projector (or open a link) and play in their phone's browser. Nothing to install and nothing to sign up for.
Does it work in PowerPoint or Google Slides?
In PowerPoint, yes: open the Decka add-in on a slide and choose the Classroom tile. Google Slides is not supported yet; there you present from Decka itself. Students play from their phones either way.
How many students can play at once?
Up to 50 participants per live activity on the free plan, 150 on Pro, and 300 on Badass.
More game theory games to run live
- Prisoner's dilemma — two suspects, separate rooms
- Chicken — four seconds on a single-track lane
- The stag hunt — one day, two ways to spend it
- Battle of the sexes — one evening, two plans
- Ten rounds in the pot
- Rock, paper, scissors — two rivals and a contract
- Matching pennies — the game where you want opposite things
- All game theory activities
Ready to make your
presentations interactive?
Start free. No credit card required.