Special education actually works — students gain 0.2 to 0.4 standard deviations in three years

Researchers tracked students in Massachusetts, Indiana, and Connecticut before and after they entered special education programs and found their test scores rose sharply after placement, gaining the equivalent of several months of learning within three years. This is the first time anyone has measured special education's actual impact using data that follows individual students over time rather than comparing groups after the fact.

Special education serves one in seven U.S. students but nobody had solid evidence it actually worked. This paper closes that gap with longitudinal data from three states showing consistent gains across disability categories and subgroups. The gains persist even when you account for testing accommodations and use conservative statistical assumptions. What this means: school districts now have evidence to defend special education funding against budget cuts, and policymakers can stop treating it as an assumption and start treating it as a measured intervention.