The authors examined differential effects of interim assessments on minority and low socioeconomic status students' achievement in Grades K-6. They conducted a large-scale cluster randomized experiment in 2009-2010 to evaluate the impact of Indiana's policy initiative introducing interim assessments statewide. The authors used 2-level models to analyze the single-grade data and determine whether interim assessments interacted with student ethnicity, socioeconomic status, gender, or school composition (i.e., percent of minority or disadvantaged students). The authors also combined estimates across grades using fixed effects meta-analysis. Results indicated little evidence about differential effects. The majority of interaction estimates were insignificant and close to zero. There is some indication that in Grades K-2 Indiana's interim assessment may have closed the Hispanic-White gap in reading. In kindergarten and Grade 3 the treatment may have widened the gap between schools with higher and lower percentages of minority students and may have reduced the gap between schools with higher and lower percentages of economically disadvantaged students in mathematics.