Social scientists have found income inequality is associated with an array of health and social problems, however the implications of income inequality for educational outcomes have not been investigated as thoroughly as other domains. In this study, I investigated how income inequality was associated with 4th grade academic achievement using state level data from the 1992 through 2019 rounds of the National Assessment of Educational Progress (NAEP). First, using an ordinary least squares modelling approach I found students in states with higher income inequality had lower average mathematics achievement, but not reading achievement. To control for stable, unobserved differences between states I estimated state fixed effects models that examined variation within states over time. States that experienced larger increases in income inequality experienced smaller increases in mathematics test scores, but not reading scores. I discuss the implications of income inequality for efforts to raise achievement among school children.