This study evaluates the effect of school district size on public high school graduation rates. The study calculates the graduation rate for each graduating class in each state between 1991 and 2002 and uses a fixed-effects model to examine the relationship between these graduation rates and changes in the size of each state's school districts during that period. The analysis indicates that decreasing the average size of a state's school districts by 200 square miles leads to an increase of about 1.64 percentage points in its graduation rate. To put this result into context, if Florida decreased the size of its school districts to the national median, it would increase its graduation rate by about 4.5 percentage points.