This article examines the impacts of Arkansas charter schools on the academic achievement of participating students. Our findings are that charter schools have small but statistically significant, negative impacts on student achievements for both math and literacy. Such negative effects, however, tend to decline with the number of years of charter operation. While Arkansas's charter law dates back to 1995, few studies have attempted to systematically evaluate charter school effects on student performance. We use longitudinal data to generate unbiased impact estimates by focusing on within-student performance differences between charter and traditional public school (TPS) students. We run the model on a rich panel of data containing standardized student performance on the Arkansas benchmark exams for roughly 1.5 million students in grades three through eight between 2002-03 and 2010-11. These comprehensive data allow us to examine the average effect of charters, how their impacts vary over time, and how the impacts differ from general student transitions between schools. Our findings coincide with results from studies using similar methodologies in Florida, North Carolina, and Texas.