Teenagers, Sleep and the School Day

For most of the twentieth century, the hours of the school day were fixed by the needs of farms, factories and working parents rather than by anything known about children. It was only in the 1990s, when sleep researchers began to measure the body clocks of adolescents directly, that a pattern became hard to ignore. Around the time of puberty, the hormone that makes the body feel sleepy is released about two hours later in the evening than it is in younger children or in adults. A fifteen-year-old who is still wide awake at ten o'clock is therefore not being difficult. The biology of the age group is simply running late. That delay would matter little if mornings were flexible, but many secondary schools begin before 8.00 am. Trials in several countries have followed students whose schools moved the first lesson back by between thirty and ninety minutes. In one trial across six schools in a single region, students in the later-starting group slept on average about forty minutes longer on school nights, and attendance at the first lesson of the day rose. Reports of drowsiness in class fell, and in a smaller number of areas so did the number of road accidents involving young drivers. Not everyone is persuaded. Head teachers point out that a later start means a later finish, which collides with sports fixtures, part-time jobs and the evening activities that many students value. Bus companies, which often serve primary and secondary schools in a single run, say that changing one timetable means changing all of them, at considerable cost. Some parents add that a household built around a seven o'clock departure cannot easily be reorganised, and that younger brothers and sisters would be left without supervision. The evidence on examination results is less clear than the evidence on sleep. Some trials report modest gains in test scores, while others find no measurable change, which may reflect the fact that results depend on many things at once. What is consistent is the improvement in mood. Counsellors in schools that changed their hours report fewer students describing themselves as constantly tired, and teachers describe calmer first lessons. In my view, the debate has been framed too narrowly. Asking whether a later start raises grades treats sleep as a tool for improving performance, when it is better understood as a basic condition of health, like nutrition. If it were shown that a school canteen served food that left students unwell, nobody would ask first whether it improved examination results. The more sensible question is whether schools should set hours that work against the body clocks of the people they serve, and the honest answer, on present evidence, is that they should not unless there is a very good reason.