This study uses an Interrupted Time Series analysis with a non-equivalent comparison group to estimate the causal effect of school finance equalization on district revenue instability. The author applies a microeconomic framework to an understudied problem in education finance and policy. In so doing, she illustrates how policies can sometimes create unintended consequences that stay with districts for multiple years. This study asks whether state finance equalization policies led to changes in long-term district revenue stability, not just immediate changes in per-pupil revenue levels. It also contributes to the literature in several ways. First, the author applies analysis of revenue instability to the education sector. Second, she examines how instability in state education funding affects school districts. Third, she assesses the long-term trend in revenue instability within a district over time, or how much fluctuation could not be predicted. Typically district-level studies compare districts at a point in time, not within-district changes over time. (Contains 1 table and 4 figures.)