It is understandably considered bad news for school choice when a study comes out finding negative effects on test scores, especially one using a “gold standard,” randomized control trial design. But context is crucial for understanding such findings, and this may be especially true for a new study of vouchers in Washington, D.C.

The researchers studied various impacts one year after families applied to the District of Columbia Opportunity Scholarship Program. Studied students participated in a lottery for vouchers, which is key because who wins or loses is random, automatically controlling for variables that can powerfully affect outcomes, such as family income or motivation levels.