We use data from a large-scale experiment conducted in Indiana in 2009-2010 to examine the impact of two interim assessment programs (mCLASS and Acuity) across the mathematics and reading achievement distributions. Specifically, we focus on whether the use of interim assessments has a particularly strong effect on improving outcomes for low achievers. Quantile regression is used to estimate treatment effects across the entire achievement distribution (i.e., provide estimates in the lower, middle, or upper tails). Results indicate that in Grades 3 to 8 (particularly third, fifth, and sixth) lower achievers seem to benefit more from interim assessments than higher achieving students.