The headmaster of the first British school to delay lessons until the afternoon has said forcing teenagers to wake up early could cause mental and public health issues.
Private school Hampton Court House, in Surrey, introduced a new timetable for sixth-formers in September 2014 following research which found that teenagers have a "biological disposition to going to bed late and getting up late".
Guy Holloway, the headmaster at Hampton Court House, said teenagers who wake up for a traditional starting time are "chronically sleep deprived".
"The cards really are stacked against them because they are overriding nature by getting up early in the morning in order to be on time for school," he said.
"Schools on a day-to-day basis are dealing with a whole range of issues - sometimes mental health issues, and I would argue a public health issue really, in terms of a nation of teenagers, particularly older teenagers, that are going to school chronically sleep deprived."
The school's timetable for 16 to 18-year-olds begins at 1.30pm and ends at 7pm. The research has found that a 7am start for a teenager is the equivalent of a 4.30am start for an adult.
One student at the school told the BBC: "I find it easier to concentrate in lessons whereas before I would sometimes be falling asleep over the first three hours of the morning.
"Here, it is so much more easy to concentrate and just focus on what I have to do."
Another student said he has become much more productive since the start time was shifted back.
"I have definitely become less of a classic teenager," he said. "In the mornings I have been a lot more co-operative and a lot nicer. I will often be helping out and I will actually be doing chores out of a want rather than a requirement."
Paul Kelly, of the Sleep and Circadian Neuroscience Institute at the University of Oxford, said in September that the mental health of young people was under "serious threat" because of sleep deprivation.
He said: "At the age of 10 you get up and go to school and it fits in with our nine-to-five lifestyle. When you are about 55 you also settle into the same pattern.
"But in between it changes a huge amount and, depending on your age, you really need to be starting around three hours later, which is entirely natural.
"This is a huge issue for society. We are generally a sleep-deprived society but the 14 to 24 age group is more sleep deprived than any other sector of society.
"This causes serious threats to health, mood performance and mental health."