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 youths 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' 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 further 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 this data shows, 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.