Classroom · Game Theory
Ten tokens each, one room, and free riding put to the test.
One whole-room pot, ten rounds, a fresh ten tokens each time. The announced rule gives every person half a token for each token contributed. Students choose privately; the projector reveals the room’s contribution pattern after each round closes.
- Up to 600 people
- About 11 min
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.
Who pays for what we share?
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
Separate the incentive to keep a token from the benefit of contributing it. Under the announced rule, contributing costs you one token and returns half to you; with more than two people, it creates more total value than keeping it. Use the class’s ten-round contribution pattern to discuss whether expectations, reciprocity or a final round changed decisions. A falling trend is a possible finding, not a required result.
- Free riding
- Dominant strategies
- Repeated games
Debrief, while the boards are still up
- 01
For one token contributed, how much comes back to you, and how much goes to the whole room? At what room size do those incentives differ?
- 02
Did contributions rise, fall or stay similar across the ten rounds? What evidence supports your explanation, and what can the anonymous chart not tell us?
- 03
What might change if contributions were named or costly punishment were allowed? Which parts of this model fit a shared fund or team project, and which do not?
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 public goods game?
A public goods game makes a shared-benefit decision visible. In this version, the teacher announces that each token kept is worth one token to its owner, while each token contributed gives half a token to every person in the room. With thirty people, one contribution therefore creates fifteen tokens of stated total benefit but returns only half a token to its contributor. That arithmetic describes the incentive model; it does not tell us what the class will choose.
The whole room plays ten rounds, with a fresh ten-token decision in each. Each phone accepts a whole-number contribution from zero to ten. During a round the board shows only previously closed rounds; afterwards it adds the contribution median, middle half and extremes. This version records contributions and their trend, not individual payoff balances. No person’s contribution is named on the chart. Compare the pattern the room actually produced, including a flat or rising line, before proposing an explanation or a different rule.
FAQ
Public goods game questions, answered
Does this use small tables or the whole room?
The whole room. Everyone answers the same contribution question over ten rounds, and one aggregate chart compares the completed rounds. There is no three-person table assignment in this version. The announced half-token return goes to each person, so the stated total benefit of a contribution depends on room size.
Do students see who contributed?
No named contribution ledger is shown. The projector displays the middle, middle half and extremes of completed rounds, not labelled individual responses. Students choose on their own phones. Ask what anonymity changes without claiming the chart identifies anybody’s motives.
How long does it take?
Ten contribution rounds plus the introduction and debrief. The saved default shows under the headline as "About N min"; review the round timing before starting.
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
- Twenty coins, take it or leave it
- 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
- Rock, paper, scissors — two rivals and a contract
- Matching pennies — the game where you want opposite things
- All game theory activities
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