Bedtime, as all parents know, is not necessarily the time when children go to sleep.
Mandy Mair, 42, of Chandlers Ford, in Hampshire, has four children with varying bedtimes and sleeping habits.
She said: "My 14-year-old, Charlotte, spends a lot of time watching Sky TV in her room but goes to sleep at 10.30pm and doesn't like getting up in the morning.
"But the 11-year-old, James, is up by 6.30am, even if it's the weekend and he has been up until 10pm.
"The eight-year-old, Emily, goes to bed by 8pm and is really grumpy the next day if we've let her stay up. But there are children in her class going to bed at 6.30pm and going straight to sleep."
Her youngest child, Benjamin, 15 months, has a bedtime of 6.30pm and a two-hour nap during the day.
The TES survey of 500 parents found that after going to bed, children generally do not put out the light for another 15 to 30 minutes. The survey also found that:
* one in three watches TV
* a quarter watch films on DVD or video
* one in eight has access to the internet, and:
* one in 10 plays computer games.
Despite the differences in bedtimes according to age, children of all ages tend to wake between 6.45am and 7.30am.
Primary-aged children have between 10 and 11 hours' sleep on school days; 11 to 14-year-olds have about nine hours', and 15 and 16-year-olds have eight to nine hours'.
A common bedtime for children in key stage 4 is 10pm, but 4 per cent regularly stay up beyond 11pm. Almost half of five to 14-year-olds were so tired that they were asleep within 15 minutes; one in 10 infants did not sleep until after 9pm; and one in 10 juniors was still awake at 9.45pm.
Parents tend to decide bedtimes for primary-age children, but this changes when they go to secondary school.
Almost one in four 11 to 14-year-olds is allowed to set their own bedtime and nearly half of 14 to 16-year-olds do so, with girls more likely than boys to be allowed to choose their own bedtime.
The TES survey found that children who set their own bedtimes did not go to bed significantly later than children who did not. Almost half of secondary pupils who set their own bedtime were in bed by 9.45pm.
But bedtime is not just a matter between parents and children. Home-school agreements can also include bedtimes or minimum hours. In the survey, 8 per cent of state schools and 18 per cent of independent schools did so. Four in 10 parents thought that schools should set bedtimes or minimum hours of sleep.
Calverton primary, in Beckton, east London, has asked parents to agree to send their child to bed at a reasonable time on school days, but it does not specify the times.
Nicole Janssen, deputy head of the 470-pupil school, said: "If a child is looking tired, the teacher can flag it up with members of the senior management team, who contact parents."
Jo Harthill, head of Mount Pleasant primary, Dudley, said: "We have some children coming in with big bags under their eyes because they've been watching videos until early in the morning.
"But I don't think a home-school agreement should include bedtimes. I'm not sure that is a school's role."