We test three hypotheses about the role of housing affordability in child cognitive achievement, behavior, and health. Using longitudinal data from the Panel Study of Income Dynamics, we apply both propensity-score matching and instrumental-variable modeling as identification strategies and test the sensitivity of results to omitted variable bias. The analysis reveals an inverted-U-shaped relation between the fraction of income devoted to housing and cognitive achievement. The inflection point at approximately 30% supports the long-standing rule-of-thumb definition of affordable housing. There is no evidence of affordability effects on behavior or health.