Although rearranging school organizational features is a popular school reform, little research exists to inform policymakers about how grade spans affect achievement. This article examines how grade spans and the school transitions that students make between fourth and eighth grade shape student performance in eighth grade. The authors estimate the impact of grade span paths on eighth-grade performance, controlling for school and student characteristics and correcting for attrition bias and quality of original school. They find that students moving from K-4 to 5-8 schools or in K-8 schools outperform students on other paths. Results suggest four possible explanations for the findings--the number and timing of school changes, the size of within-school cohorts, and the stability of peer cohorts. (Contains 11 tables and 21 notes.)