Switching off your mobile at 9pm could make you far more productive at school the next day, researchers have found.

A team the University of Washington say using your phone late at night can seriously damage your sleep – and your performance at school the next day.

They advise students to switch off – or risk being ‘less engaged’ at school the next day.

‘Smartphones are enormously valuable for helping students to fit work activity into times and places outside of the school,’ says Christopher Barnes, an assistant professor of management at the University of Washington’s Foster School of Business, who led the research, which will be published in the journal Organizational Behaviour and Human Decision Processes later this year.

‘Our new research indicates the greater connectivity comes at a cost: using a smartphone to cram more work into a given evening results in less work done the next day,’ he says.

‘The reason for this, as we’ll explain, is that smartphones are bad for sleep, and sleep is very important to effectiveness as a student.

‘Unfortunately, smartphones are almost perfectly designed to disrupt sleep.

‘Because they keep us mentally engaged with work late into the evening, they make it harder to psychologically detach from the most pressing cares of the day so that we can relax and fall asleep.

‘Perhaps the most difficult aspect of smartphones to avoid is that they expose us to light, including blue light.

‘Even small amounts of blue light inhibit the sleep-promoting chemical melatonin, meaning that the displays of smartphones are capable of producing this effect.’

‘The more important the messages and chatting, the more important it is to work with a fresh brain,’ they say.

‘We would do well to remember that, and not let our phones call the shots’