A small subset of education studies analyzes school data collected seasonally (separating the summer from the school year). At first, this work was primarily known for documenting learning loss in the summers, but scholars have since recognized that observing how inequality changes between summer and school periods provides leverage for understanding how schools influence inequality. Results based on this analytic technique confirm current views in some ways, but in other ways the patterns challenge existing wisdom. For example, Black/White gaps in math and reading skills often grow faster when school is in versus out, consistent with the view that schools exacerbate racial inequality. But socioeconomic gaps produce the opposite pattern, suggesting that schools are compensatory across this dimension. In this review, I consider the logic behind seasonal research, the empirical patterns it has produced, and the kinds of new questions it motivates.