Spillover Snap

Spillover Snap: externalities, social costs and social benefits for Edexcel IGCSE Economics

This free game is part of our Pearson Edexcel IGCSE Economics (4EC1) course for exams in EXAM YEARS 2027-2030.

Who really pays?

Spillover Snap is a free 3D game about externalities for Pearson Edexcel International GCSE Economics (4EC1). It covers specification point 1.1.6 (a) to (e): the definition of external costs and examples of them (pollution, congestion and environmental damage), the definition of external benefits and examples of them (education, healthcare and vaccinations), and the formulas social costs = private costs + external costs and social benefits = private benefits + external benefits.

You are the photographer for the Vale Herald, a local paper in a valley town, and this week’s front page asks one question: who really pays? Every deal in the valley has a glowing ring on the ground round the people in it: the producer, the consumer and anyone they pay. Your job is to photograph the spill-overs that leak out of the ring and land on third parties, the people outside the deal who never agreed to it.

Snap the spill-overs, leave the private stuff

• Greystone Cement (external costs of production): dust from the chimney settles on the houses of Hill Row and families start coughing (pollution); a convoy of cement lorries crawls along the valley road with cars and the bus stuck behind it (congestion); waste from the works pours into the river and kills the fish (environmental damage).
• Vale Health Centre (external benefits of consumption): the free flu jabs protect more than the people who have them. Mo is less likely to pass flu on, so his colleagues stay well; Leo’s class stays well and the school stays open; Priya’s grandparents are less likely to catch flu from her.
• Vale College: college leavers give Vale Engineering skilled workers it didn’t pay to train, and firms across the valley get a more productive workforce.
• Vale Hospital: when Dev is treated, his mum no longer has to care for him and can go back to work.

Not everything is a spill-over. Payday at the works, a limestone delivery the firm pays for, the protection a person gets from their own jab and the higher pay a student gets from their own qualification all stay inside the deal: they are private costs and private benefits, so you leave them. Every photo prints with what it cost or gained in million Zed.

Stack the tower: private + external = social

After each case you drop your photos onto a tower in front of the Vale Herald’s infographic board. Greystone’s private costs go in first (wages 40, limestone 30 and electricity 20 million Zed), then the external costs on top (9 + 4 + 2), and the tower shows social costs = 90 + 15 = 105 million Zed. The flu jabs give social benefits = 8 + 5 = 13 million Zed. At the college the tower has a dashed outline for social benefits of 30 million Zed above private benefits of 20 million, so you can see the formula turned round: external benefits = social benefits − private benefits = 10 million Zed, and the same works for costs.

Dara, the picture editor, explains why it matters: a firm only looks at its own private costs and people only weigh up their own private benefits, so a market makes too much of a good with external costs and too little of a good with external benefits, such as vaccinations.

Learn it, then prove it

Everything is taught in the game before you are tested on it. Quick checks ask you to calculate social costs, find a missing external cost, pick an external benefit of consumption and choose the definition of external costs that would get both marks. Snapping a private moment, missing a spill-over or picking a wrong answer brings up a short explanation with a “Why not?” and a link to the lesson. A final deadline rush mixes everything against the clock, and the end screen is a front page with your photos, your rank, your best score and a summary of the definitions and formulas.

The game takes about 7 to 9 minutes. It works with a mouse, a touch screen or the keyboard (arrow keys aim, Tab jumps to the next frame, Space snaps), needs no login and runs on school Chromebooks, so it’s easy to use as a starter or a plenary in an economics lesson.