China's Gaokao

China's Gaokao is the single most consequential exam on this list, dictating the entire academic future of 12 million students in just two days. That annual cohort exceeds the population of New York City, and the pressure drives teen anxiety and depression rates 30% higher than the global average for adolescents, with suicide a documented risk. This system crushes more young lives than the runner-up SAT, which at least measures privilege over merit. Concrete data: 12 million test-takers yearly, with mental health impacts 30% above global norms.