http://hechingered.org/content/how-summer-increases-the-achievement-gap_5072/ I've seen graphs of the effect summer has on student performance and it's sobering, especially when data are disaggregated for high- and low-SES students. According to some measures, low-SES students learn at the same rate during the school year as high-SES students, and almost all of the achievement gap between the two accumulates during the summer months.