Teach it. Check it. Revisit it.

Teacher guide

Audience: 13–18. Session: 45 minutes. Preparation: 10 minutes: paper and a calculator.

Prerequisites: Understand costs, benefits and basic market tradeoffs.

1. Spend 5 minutes asking learners to predict the result and explain their reasoning.
2. Use most of the session for the student activity. Ask learners to show calculations and name assumptions.
3. Reserve 5 minutes for the exit questions. Discuss why the answer follows, not just whether it matches.
4. Return to the follow-up next week without showing today’s answers first.

Student activity

A fictional activity creates $12 of benefit, $8 of private cost and $6 of pollution damage per unit. Compare the private and social net benefits. Assume all values measure comparable incremental benefits and costs.

Write your prediction, calculation, explanation and one assumption you would check in a real situation.

Exit quiz

1. What is the private net benefit? What is the social net benefit?
2. Does identifying a negative externality tell us the best policy automatically?

Teacher answers and reasoning

1. Private net benefit is $4. Social net benefit is $12 − $8 − $6 = −$2.
2. No. Compare possible policies, measurement uncertainty, enforcement costs and who bears each burden.

For each response, check the method, the result and the explanation. A correct number with an incorrect explanation needs another example.

Next-week review

Next week, change pollution damage to $2. Recalculate social net benefit ($2) and explain why the conclusion changed.

Facts, assumptions and policy debate

The example’s arithmetic follows its assumptions. The damage estimate and the choice of a remedy need evidence and explicit value judgments.

Ask: what is calculated, what is assumed, and what is a judgment about priorities?