An earlier school hour means more time to work on academic projects later in the day, as there is no hurry to get things done — a problem a late-riser might face would be procrastination.
Accordingly, Cantillon represents in my view one of the important stages, and in many respects perhaps even the primary stage, in the straight developmental path of knowledge, from which the disciples of the "schools" have always deviated in one way or the other. The Physiocrats and, like them, at least some of the later classical writers, were thus hindering rather than promoting progress, while the great strides were always made outside the schools and mostly in opposition to them. In terms of really original insights of permanent value to our discipline, Cantillon offers us more than any other author writing before 1776, the year in which the works of Smith and Condillac appeared, and hence more than the Physiocrats, even though their presentation of the circular flow—which one could validly describe as a systemization of Cantillon's ideas—had greater visual impact and proved more influential for the time being. Whether one therefore calls Cantillon founder of economic science or not, is a matter of little consequence. Determining the point of origin of a science always involves a high degree of arbitrary choice. The fact that we must rank him as one of the great scholars of our discipline will hopefully not be doubted by any reader of the The actual extent of his influence on the development of economic science is, of course, another question and one which is extremely difficult to answer. Before attempting to do so, let us record the little that is known of Cantillon's life and the history of his manuscript from the time of his death until its publication.
As a final check on the accuracy of my results, I perform analyses that compare the achievement of individual students to their own achievement in a different year in which the middle school they attended started at a different time. For example, this method would compare the scores of 7th graders at a school with a 7:30 start time in 2003 to the scores of the same students as 8th graders in 2004, when the school had a start time of 8:00. As this suggests, this method can only be used for the roughly 28 percent of students in my sample whose middle school changed its start time while they were enrolled.
My first method compares students with similar characteristics who attend schools that are similar except for having different start times. The results indicate that a one-hour delay in start time increases standardized test scores on both math and reading tests by roughly 3 percentile points. As noted above, however, these results could be biased by unmeasured differences between early- and late-starting schools (or the students who attend them).
To deal with this potential problem, my second approach focuses on schools that changed their start times during the study period. Fourteen of the district’s middle schools changed their start times, including seven schools that changed their start times by 30 minutes or more. This enables me to compare the test scores of students who attended a particular school to the test scores of students who attended the same school in a different year, when it had an earlier or later start time. For example, this method would compare the test scores of students at a middle school that had a 7:30 start time from 1999 to 2003 to the scores of students at the same school when it had an 8:00 start time from 2004 to 2006. I still control for all of the student and school characteristics mentioned earlier.
Previous research tends to find that students in early-starting schools are more likely to be tardy to school and to be absent. In Wake County, students who start school one hour later have 1.3 fewer absences than the typical student—a reduction of about 25 percent. Fewer absences therefore may also explain why later-starting students have higher test scores: students who have an early start time miss more school and could perform worse on standardized tests as a result.
Of course, increased sleep is not the only possible reason later-starting middle-school students have higher test scores. Students in early-starting schools could be more likely to skip breakfast. Because they also get out of school earlier, they could spend more (or less) time playing sports, watching television, or doing homework. They could be more likely to be absent, tardy, or have behavioral problems in school. Other explanations are possible as well. While my data do not allow me to explore all possible mechanisms, I am able to test several of them.
I find that students who start school one hour later watch 12 fewer minutes of television per day and spend 9 minutes more on homework per week, perhaps because students who start school later spend less time at home alone. Students who start school earlier come home from school earlier and may, as a result, spend more time at home alone and less time at home with their parents. If students watch television when they are home alone and do their homework when their parents are home, this behavior could explain why students who start school later have higher test scores. In other words, it may be that it is not so much early start times that matter but rather early end times.
To further investigate how the effect of later start times varies with age, I estimate the effect of start times on upper elementary students (grades 3–5). If adolescent hormones are the mechanism through which start times affect academic performance, preadolescent elementary students should not be affected by early start times. I find that start times in fact had no effect on elementary students. However, elementary schools start much later than middle schools (more than half of elementary schools begin at 9:15, and almost all of the rest begin at 8:15). As a result, it is not clear if there is no effect because start times are not a factor in the academic performance of prepubescent students, or because the schools start much later and only very early start times affect performance.
The typical explanation for why later start times might increase academic achievement is that by starting school later, students will get more sleep. As students enter adolescence, hormonal changes make it difficult for them to compensate for early school start times by going to bed earlier. Because students enter adolescence during their middle-school years, examining the effect of start times as students age allows me to test this theory. If the adolescent hormone explanation is true, the effect of school start times should be larger for older students, who are more likely to have begun puberty.
Later school start times have been touted as a way to increase student performance. There has not, however, been much empirical evidence supporting this claim or calculating how large an effect later start times might have. My results indicate that delaying the start times of middle schools that currently open at 7:30 by one hour would increase math and reading scores by 2 to 3 percentile points, an impact that persists into at least the 10th grade.
I also looked separately at the effect of later start times for lower-scoring and higher-scoring students. The results indicate that the effect of a later start time in both math and reading is more than twice as large for students in the bottom third of the test-score distribution than for students in the top third. The larger effect of start times on low-scoring students suggests that delaying school start times may be an especially relevant policy change for school districts trying to meet minimum competency requirements (such as those mandated in the No Child Left Behind Act).