This is the four-group version of The Common, built for teachers to run with a whole class. Split your students into four groups, give each group one of the four herding families of Nethergrove, and let them make their own decisions on a shared village green - season by season, in front of the room.
Each group turns out as many animals as they choose. The green has to feed all of them. What happens after that is up to the room.
Each group represents one of the four herding families: the Hartleys, the Dunns, the Pikes, the Quills. They make the family's grazing decisions for the whole game.
Five seasons under no rules at all, then a class discussion, then five more under whatever quota the room agrees.
Each group picks their number for the season. Numbers are revealed all at once. No group sees another group's choice until the reveal.
Type the numbers in directly, or run it as a hand-count - groups raise fingers, you tap the tile. Switch at any time.
This isn't a lesson where the teacher tells the students what happens. It's a lesson where the students do what happens, and then talk about why. By the end, the room will have worked out for itself:
Split the class into four groups of roughly equal size. Hand each group a family name - Hartley, Dunn, Pike, Quill - and tell them they're a herding family in Nethergrove. They share a common green with the other three families. Their job, each season, is to decide how many animals to turn out.
Each season the green can carry up to 16 animals in total before the grass starts to wear away faster than it can grow back. The four families don't have to agree on anything. Each decides for itself.
For each of the first five seasons:
The room will notice the green going backwards. That's the lesson - let them notice, don't preempt it.
This is the moment the whole sim is built around. After Season 5, the screen shows the state of the green and asks: what rule should the village try?
Open the floor. Let the room propose a rule. The standard textbook answer is a quota of 4 animals per family - the carrying capacity of 16 divided across four herders. The class might propose that. They might propose something else. You set the quota with the picker.
Then the second spell begins. Same green, same families, one new rule. Watch what changes.
The debrief screen shows both spells side by side: total animals turned out, state of the green, how each family did. It's a built-in springboard for the closing conversation - which one was a market failure? What did the rule do? Where else does this logic show up?
After five seasons of that, the families of Nethergrove gather to talk it over. Open the floor to your class - what rule should the village try?
The standard suggestion is a per-family quota: each family allowed at most a fixed number of animals per season. Take a suggestion from the room. Set it below. Then return to the green.
Each family may turn out at most this many animals per season:
The green can carry 16 animals across the four families. A quota of 16 is the total grazing the rule will allow.
How each group's family fared across the two spells.
The green is a common resource: no one owns it, and no one can be kept off. Two features make that combination dangerous. It's non-excludable - no family can be shut out. And it's rival - grass one animal eats is grass another cannot.
Each season, every group could see that turning out more animals would earn their family more milk and wool that season. The cost - wear on the grass - fell on the whole green, on every family, on every season still to come. The gain was private. The cost was shared.
That's the tragedy of the commons. It isn't a story about bad herders. It's a story about how a shared resource, with no rule on its use, falls apart even when everyone is acting reasonably.
A quota doesn't change the green or the families. It changes the choice. By capping every family's herd, it stops the shared cost from ever growing faster than the grass can mend. The same logic appears in the wider world:
Each fleet is capped, so total catch stays within what the stock can replace.
Each emitter faces a cost, so the shared atmospheric harm is no longer free to them.
Each driver pays for the journey, so the cost of a slower commute for everyone is faced by the person making it.
Give the resource an owner with a stake in its future, and the over-use problem changes shape.