Michigan's Great Start Readiness Program (GSRP) is a state-funded pre-K program that serves at risk four-year-old children across the state. Utilizing longitudinal data from 1,394 children in a mid-sized urban school district, we conducted regression analyses and piecewise linear growth models to examine the growth trajectory of GSRP children and non-GSRP children at each grade level from kindergarten to third grade in both reading and math. The results of regression analyses showed that, after accounting for other variables, participation in GSRP was statistically significantly associated with higher scores on Measure of Academic Progress (MAP) measures at various time points, ranging from 0.22-0.46 standard deviations (SD) in math and 0.31-0.49 SD in reading. The results of piecewise linear growth models illustrated that GSRP children had a statistically significantly faster monthly growth rate than non-GSRP children during the kindergarten year. However, the growth rates were not significantly different during the first, second, and third grade.