Public Goods and Free Rider Activity

Use this 35 minutes classroom activity to teach public goods and free riders through one concrete decision. Students experience the conflict between a positive social return and a negative private return to voluntary contribution. Students create the economic outcome themselves before naming the model. Resist explaining the result during the first round. The debrief is where the experience becomes economics.

The classroom prompt

Students secretly keep or contribute each token. After a round, multiply the group contribution by 0.4 and pay that amount to every member. Repeat after groups may discuss, then after adding one policy rule.

Put the question where every student can see it and do not supply vocabulary before students commit to an answer. Their first explanation becomes the evidence you use during the debrief.

Materials and setup

Give each student 10 tokens. In groups of four, every contributed token pays 0.4 token to every group member.

Open the externalities sandbox if you want students to test the same idea on an interactive model after the paper task. A projected version is enough; students do not need accounts for this lesson.

Run the lesson

Answer key and teacher moves

• One contributed token returns 0.4 to its contributor, so the contributor privately loses 0.6 relative to keeping it.
• The same token returns 0.4 to each of four people, a total social return of 1.6.
• Full contribution maximizes group tokens, while individual free riding is privately tempting in a one-shot anonymous round.
• Communication or repeated interaction may raise contribution but does not remove the underlying incentive problem.

Do not give credit for the correct direction alone. Ask students to name the changed determinant, identify the curve or quantity that changes, and connect the change to the final outcome. A complete explanation contains a cause, a model move, and a result.

What to collect

Collect each student's round-by-round choices and a paragraph explaining private versus social incentives.

Most likely misconception: Students say contribution is irrational overall because the contributor receives less than one, ignoring benefits to the other members.

Support and extension: Use whole-number payouts by multiplying all tokens by ten. Extend by changing group size while holding the private return fixed.

A clean closing question

End with: What changed, what stayed fixed, and what evidence proves your conclusion? That sentence works as the final written check because it forces students to separate a cause from the movement it produces. Collect it, scan for the misconception above, and use the first three minutes of the next class to repair the pattern if needed.

This resource is ready to copy into a slide, handout, or LMS assignment. If you assign it for points, publish the success criteria before students begin: correct model, correct direction, and an explanation that links the two.