A recent study by RAND estimated that earlier start times in the US, where classes often begin well before 8am, would add $83bn to the national economy over a decade, and $140bn over 15 years, by raising students’ academic attainments and reducing illness, according to Financial Times.

The RAND report is the latest manifestation of a growing concern that inadequate and ill-timed sleep is causing a public health disaster in the industrialised world. Matthew Walker, neuroscience professor at the University of California, Berkeley, describes a silent sleep loss epidemic in his book Why We Sleep, published last summer. He says changing social and employment patterns and new sleep-disrupting consumer products such as smartphones, are “having a catastrophic impact on our health, our life expectancy, our safety, our productivity and the education of our children.”

Students in secondary schools are particularly vulnerable as a result of biological changes during adolescence, which push back their circadian rhythm — the natural body clock that controls the sleep-wake cycle — by as much as three hours compared with the adult cycle.

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