Magnitudes of score differences produced within sessions in a cooperative exchange procedure.

Adults sat across from each other in a lab. They pressed buttons to earn coins for both themselves and the partner.

A computer showed each person's score after every press. The session ended when a timer hit zero.

The researchers added rules: sometimes a small fee punished making the scores unequal. Other times a warning light said the game would end soon.

Without the fee, people kept the two scores almost equal. Minute-by-minute adjustments kept the gap tiny.

When the fee arrived, one player quickly pulled ahead. The gap stayed large for the rest of the session.

A final warning light brought the scores back to equal again. People rushed to even things out before time ran out.

Weiner (1977) looks opposite at first. In that study, people pressed a button that helped only the partner. That kind of 'pure altruism' faded fast. The difference is the task: keeping scores equal feels fair and stays strong, while one-way helping is fragile.

Clarke (1998) moves the same idea into competition. Proportional payoffs plus live feedback kept both players trying hard. Fixed winner-take-all prizes made the loser quit early. Together the papers show that payoff rules, not just social motives, shape whether people keep or break equality.

Mace et al. (1990) took the insight to a classroom. Students shifted their math work toward the side that paid more tokens. The lab lesson—reinforcement rate drives allocation—held true for kids and academic tasks.

You can build or break cooperation in any session by how you set the payoffs. If you want two learners to stay equal, avoid penalties that reward one for pulling ahead. If you need a quick reset, add a clear 'session almost over' cue and watch them balance the scores. Control the contingencies and you control the fairness.