Since 1906, there have been more than 40 empirical studies that have found indisputable evidence of a pattern of “summer learning loss,” particularly for low-income youth:

Students typically score lower on standardized tests at the end of summer than they do on the same tests at the beginning of summer. (Downey et al. 2004)

All young people are at risk of experiencing setbacks in math skills over the summer months. (Cooper, 1996)

Young people in high-poverty communities face much greater risks of experiencing losses.  Low-income children fall behind an average of 2-3 months in reading skills while their middle-income peers can make slight gains. (Cooper, 1996)

As losses accumulate summer after summer, lower-income students are nearly three years behind their better-off peers in reading by the time they reach fifth grade. (Alexander et al. 2007)

Cumulative losses in reading over the summer months during the elementary school years contribute to the persistent achievement gap between young people from lower- and higher-income households. Two-thirds of the ninth grade achievement gap in reading can be explained by unequal access to summer learning opportunities in the elementary school years. (Alexander et al. 2007)

Young people face potential health and nutritional setbacks as well. Children gain weight two or three times faster during the summer months, gaining as much weight during the summer as they do during the entire school year. The problem is more pronounced for African-American and Hispanic kids, as well as those who are already overweight. (von Hippel, et al. 2007)

Source: National Summer Learning Association