Testing Ten Stylized Facts About Public Goods Games. A Large-Scale Replication Using Classroom Data

We test the replicability of ten stylized facts about voluntary contributions to public goods using a large crowd-sourced dataset of classroom experiments on the classEx platform. Our sample comprises 81,391 contribution decisions by 10,891 players across 377 sessions in 16 countries (2019-2025). Five facts replicate: initial contributions above Nash (37.6% of endowment), non-zero final-round contributions (38.7%), conditional cooperation as the modal behavioral type, imperfect matching, and cross-country heterogeneity. One is partially confirmed (a modest end-game effect) and one is weakly supported (a positive MPCR effect, sensitive to country fixed effects). Three do not replicate. Contributions follow a hump-shaped trajectory - rising through round 5, plateauing, then gently declining - rather than the canonical decline. Only 34.4% of players free-ride in the final round (vs. the laboratory benchmark of over 70%), while a substantial minority (22.1%) sustain full cooperation. Societal indicators do not predict country-level cooperation, partly because cross-country variation explains only 0.8% of individual contribution variance - an order of magnitude less than organization-level heterogeneity (6.8%). Taken together, the canonical behavioral building blocks of the public goods game reproduce in the classroom, whereas several of its dynamic and cross-country regularities - most notably the absence of the canonical decline - do not. (Includes Online Appendix with experimental interface and additional figures.)