The learning curve: Revisiting the assumption of linear growth across the school year

Important educational policy decisions, like whether to shorten or extend the school year, often require accurate estimates of how much students learn during the year.  Yet, related research relies on a mostly untested assumption: that growth in achievement is linear throughout the entire school year.  We examine this assumption using a data set containing math and reading test scores for over seven million students in kindergarten through 8th grade across the fall, winter, and spring of the 2016-17 school year. Our results indicate that assuming linear within-year growth is often not justified, particularly in reading. Implications for investments in extending the school year, summer learning loss, and racial/ethnic achievement gaps are discussed.