A new study was conducted on teenage sleeping patterns and a physical reason for the delay in bedtimes has been found.
The study involved 13 boys and girls between ages 10 and 16; seven were pre-teens, the rest teenagers. All underwent 36 hours of sleep deprivation in a lab as their brainwaves were monitored.

It has been found that a person’s “sleep pressure” rate, the biological trigger that causes sleepiness, slows down in adolescence. The study suggests that as children mature, their internal, chemically driven pressure to sleep builds up more slowly and that their need for sleep arrives at least two hours later.
They have also developed another theory concerning a hormone called melatonin. They believe that this hormone that informs the body that it is night time is released up to two hours later in the day when people are in their teens compared with when they are children.

However, other experts believe that the theory about the role of melatonin is exaggerated and say that sleeping patterns in adolescents were bore behavioral that biological in nature.