In the face of school crowding and fears about inequality-inducing summer learning loss, many schools have started to adopt multi-track year-round school calendars, which keep the same number of school days, but spread them more evenly across the calendar year. This change allows schools to support a larger student population by rotating which students are on break at any point in time. While year-round schooling can save money, the impact on academic achievement is uncertain and only recently have large-scale studies become available for policy makers. This brief examines research on the effects of multi-track year-round schooling, focusing on two rigorously executed case studies. This research gives little support for claims that year-round schooling will boost student achievement. Except as a remedy for highly over-crowded schools, year-round schooling seems to have little impact on achievement, and has even been shown to decrease achievement, especially among the most high-risk student populations.