Better sleep may lead to improved exam results along with an increased ability to concentrate and positive changes to mood and health.

Published in the July issue of Archives of Paediatrics & Adolescent Medicine, the study by researchers in the paediatric sleep clinic Hasbro Children's Hospital in Providence revealed that allowing teenagers to sleep later in the morning may be beneficial.

Judith Owens, lead author, said that many factors such as after school activities push bedtimes later.

She told the Wall Street Journal: "On a practical level this means that the average adolescent has difficulty falling asleep before 11pm."

The study showed that the average teenager needed nine hours of sleep at night, however to get to school for 8am, most would wake up at around 6am.

According to findings, a later start time led to better sleep and improved motivation.

A recent US study also called for a later start to school times as findings showed there was an increased rate in car accidents in schools that started early.