In general, low-income students lose around 3 months of grade-level equivalency during the summer months. Middle income students lose about 1 month of grade-level equivalency over the summer. Thus, the achievement gap widens, due to out-of-school influences and lack of summer learning opportunities.
Throughout the 20th century, numerous studies examined general learning loss among all students during the summer months. A meta-analysis of 39 studies conducted since 1978 found that in the absence of school, all students score lower on standardized math tests at the end of the summer as compared to their performance on the same tests at the beginning of summer. This loss was most acute in factual and procedural learning such as mathematical computation, where an average setback of more than two months of grade-level equivalency was observed among both middle- and lower-class students. In reading and language, however, substantial differences were found between middle- and lower-class students. Whereas middle-class students showed a nonsignificant gain in reading scores, lower-class students showed a significant loss that represented a gap of about three months of grade-level equivalent reading skills between middle- and lower-class students.
These results are consistent with other researcher's findings that a family’s socioeconomic status affects children’s achievement scores almost exclusively when school is closed. Barbara Heyns’ 1978 landmark study of 2,978 6th and 7th graders in the Atlanta city public schools was the first thorough investigation of summer learning. Heyns found that while poor children and black children came close to keeping up with middle-class children in cognitive growth when school was in session, they lagged far behind during the summer.
Researchers Doris Entwistle and Karl Alexander extended Barbara Heyns’ line of research through the Beginning School Study (BSS) in 1982. BSS compared the school-year and summer achievement gains of 790 youth across 20 of Baltimore’s public schools from the beginning of first grade in 1982 through the end of elementary school. The study also tracked these students’s progress through high school and college. They found that in year nine, the low-socioeconomic status (SES) group’s Reading Comprehension average lagged 73 points behind the high-SES group’s on the California Achievement Test (CAT-V). About a third of the 73 points difference (27 points) was in place when the students started first grade. After the first grade, the low-SES students fall farther behind each year, with the gap reaching a plateau of around 70 points in the 5th grade. The remaining two-thirds of the 73 point gap accumulate over the course of the elementary and middle school years, with a staggering 48.5 points being attributed to the cumulative summer learning gap from the five elementary years. As these data show, virtually the entire achievement gap reflects differences between low-SES and high-SES students’ home environments, with cognitive gains during the school year being relatively equal between both groups.
Researchers from The Ohio State University extended summer learning gap research further by conducting a national study of 17,000 kindergarten and first grade children from the Early Childhood Longitudinal Study. The authors confirmed earlier findings of an unequal starting point, showing that a standard deviation’s advantage in SES predicts a 1.77 month advantage in initial reading skill on the first day of kindergarten. The authors also confirmed that the SES achievement gap continues to grow after schooling starts, with summer learning accounting for the vast majority of the difference. While the average kindergarten learning rate was 1.65 test points per month, a standard deviation’s advantage in SES predicted a relative gain of 0.16 points per month during summer, 0.07 points per month during kindergarten, and 0.05 points per month during first grade.