For this portion of the study, we compare KIPP students with two groups of district school students: all those attending non-KIPP middle schools in the same district, and a smaller comparison group of students attending middle schools that accepted an above-average number of students from the feeder elementary schools. In other words, if students from feeder elementary schools eventually attend five different non-KIPP middle schools, the two most commonly attended of these middle schools would be included in the “comparison” middle-school group.
We find that, on average, KIPP middle schools admit students who are similar to those in other local schools, and patterns of student attrition are typically no different at KIPP than at nearby public middle schools. In both groups of schools, students who leave before completing middle school are substantially lower-achieving than those who remain. KIPP schools replace fewer of these students in the last two years of middle school, however, and, compared to district schools, KIPP schools tend to replace those who leave with higher-achieving students. Nonetheless, while this difference in replacement patterns is noteworthy, it cannot account for KIPP’s overall impact on student achievement. In particular, the literature on peer effects suggests that KIPP’s student replacement pattern could produce only a small fraction of KIPP’s actual impact on student achievement. A large part of KIPP’s cumulative effect occurs in students’ first year of enrollment, before attrition and replacement could have any effect.
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The primary rationale given for start times affecting academic performance is biological. Numerous studies, including those published by Elizabeth Baroni and her colleagues in 2004 and by Fred Danner and Barbara Phillips in 2008, have found that earlier start times may result in fewer hours of sleep, as students may not fully compensate for earlier rising times with earlier bedtimes. Activities such as sports and work, along with family and social schedules, may make it difficult for students to adjust the time they go to bed. In addition, the onset of puberty brings two factors that can make this adjustment particularly difficult for adolescents: an increase in the amount of sleep needed and a change in the natural timing of the sleep cycle. Hormonal changes, in particular, the secretion of melatonin, shift the natural circadian rhythm of adolescents, making it increasingly difficult for them to fall asleep early in the evening. Lack of sleep, in turn, can interfere with learning. A 1996 survey of research studies found substantial evidence that less sleep is associated with a decrease in cognitive performance, both in laboratory settings and through self-reported sleep habits. Researchers have likewise reported a negative correlation between self-reported hours of sleep and school grades among both middle- and high-school students.