In large urban districts, schools enrolling more white students tend to have higher performance ratings. We use an instrumental variables strategy leveraging centralized school assignment to explore this relationship. Estimates from Denver and New York City suggest the correlation between school performance ratings and white enrollment shares reflects selection bias rather than causal school value-added. In fact, value-added in these two cities is essentially unrelated to white enrollment shares. A simple regression adjustment is shown to yield school ratings that are uncorrelated with race, while predicting value-added as well or better than the corresponding unadjusted measures.