Using a national sample of kindergarten to eighth grade students from Catholic and public schools who took MAP Growth assessments, we examine achievement growth over time between sectors. Our findings suggest that while Catholic school students score higher in math and reading than public school students on average, they also enter each school year at a higher level. Public school students close this gap to some degree during the school year. Additionally, these patterns varied by age and subject. Catholic school students in the earlier grades show less growth in both reading and math during the academic year compared to their public school peers, but in middle school, growth patterns in math were comparable across sectors.