It is what teenagers have suspected all along. Too much homework is just not beneficial.
Although teachers and parents might think that extra learning helps youngsters get to grips with a subject, new research suggests that 60 minutes of study will bring the best results.
In fact, forcing youngsters to continue working for more than 90 minutes could actually make their grades worse.
Under the previous Labour government, schools were encouraged to set up to two and half hours of homework each night for those aged 14 to 16.
But the guidance was axed by Michael Gove, the former Education Secretary, after head teachers said they should have the final say in work outside of school hours.
Researchers from the University of Oviedo in Spain looked at the maths and science of performance of 7,725 teenage pupils from state and private schools in northern Spain.
The students were given questionnaires asking how often they did homework and how much time they spent on various subjects.
They were also asked whether they did their homework alone or whether they had help and, if so, how often.
“Our data indicate that it is not necessary to assign huge quantities of homework, but it is important that assignment is systematic and regular, with the aim of instilling work habits and promoting autonomous, self-regulated learning,” said co-author Dr Javier Suarez-Alvarez.
“Homework should not exclusively aim for repetition or revision of content, as this type of task is associated with less effort and lower results.”
“The data suggest that spending 60 minutes a day doing homework is a reasonable and effective time.”
Researchers found that the total amount of homework assigned by teachers was a little more than 70 minutes per day on average.
But the discovered that when teachers assigned 90 to 100 minutes of homework, maths and science results actually began to decline.
Even the small gains which were made by some pupils who worked longer were not worth the extra effort, the researchers warned.
“For that reason, assigning more than 70 minutes of homework per day does not seem very efficient,” said Dr Suarez-Alvarez.
Academic performance in math and science was measured using a standardised test with adjustments made to account for gender and socioeconomic background.
The team found that students who worked on their own, without help, performed better.
Pupils who did their homework on their own scored 54 points higher than those who asked for frequent or constant help.
Previous studies have found that self-regulated learning is lined to academic performance and success.
“The conclusion is that when it comes to homework, how is more important than how much,” said Dr Suarez-Alvarez.
Under old guidelines introduced in 1998, primary schools were told to set an hour of homework a week for children aged five to seven, rising to half an hour a night for seven-to-11-year-olds. Secondary schools were told to set 45 to 90 minutes a night for pupils aged 11 to 14, and up to two-and-a-half hours a night for those aged 14 to 16.
Research last year suggested that around one quarter of British parents do homework for their children because they believe they have too much, or deem it to be too difficult.
Last year headteacher Dawn Moore, head of King Alfred School, north London, warned that primary-age pupils should be effectively exempt from homework because it is damaging childhood and creating tensions between families.
Teachers should stop setting work until the final few years of primary education to prevent pupils being overloaded at a young age, she argued.
The new research was printed in the Journal of Educational Psychology.