Sixty-seven school finance reforms (SFRs), a combination of court-ordered and legislative reforms, have taken place since 1990; however, there is little empirical evidence on the heterogeneity of SFR effects. In this study, we estimate the effects of SFRs on revenues and expenditures between 1990 and 2014 for 26 states. We find that, on average, per pupil spending increased, especially in low-income districts relative to high-income districts. However, underlying these average effect estimates, the distribution of state-level effect sizes ranges from negative to positive—there is substantial heterogeneity. When predicting SFR impacts, we find that multiple state-level SFRs, union strength, and some funding formula components are positively associated with SFR effect sizes in low-income districts. We also show that, on average, states without SFRs adopted funding formula components and increased K-12 state revenues similarly to states with SFRs.