Lots of us know we are sleep-deprived but imagine if we could fix it with a fairly simple solution: getting up later. In a speech at the British Science Festival, Dr Paul Kelley, clinical research associate at the Sleep and Circadian Neuroscience Institute at Oxford University, called for schools to stagger their starting times to work with the natural biological rhythms of their students. It would improve cognitive performance, exam results and students’ health (sleep deprivation has been linked with diabetes, depression, obesity and an impaired immune system). It follows a paper, published in 2014, in which he noted that, when children are around ten, their biological wake-up time is about 6.30am; at 16, this rises to 8am; and, at 18, someone you may think of as a lazy teenager actually has a natural waking hour of 9am. The conventional school starting time works for 10-year-olds but not 16- to 18-year-olds. For the older teenagers, it might be more sensible to start the school day at 11am or even later. “A 7am alarm call for older adolescents,” Kelley and his colleagues pointed out in the paper, “is the equivalent of a 4.30am start for a teacher in their 50s.” He says it’s not as simple as persuading teenagers to go to bed earlier. “The body’s natural rhythm is controlled by a particular kind of light,” says Kelley. “The eye doesn’t just contain