School pupils in the UK - and the parents who have to help them - get more homework than many other European countries, according to the OECD international think tank.
The OECD, which carries out the Pisa tests of school performance, has produced a comparison of homework.
It suggests teenagers in the UK put in more hours than in countries such as Finland, Germany, Sweden and Austria.
But they are far behind pupils in Singapore and Shanghai in China.
The most distinctive feature of the UK's homework hours is the social gap.
Long hours, high results?
The OECD study suggests an international pattern for the urban middle classes to have the highest amounts of time spent on homework.
But this is particularly accentuated in the UK, which has one of the widest gaps in homework hours between wealthy and disadvantaged pupils.
Andreas Schleicher, the OECD's director of education, says this is likely to widen the gap in how well pupils perform in exams as there is a link between longer homework hours and higher achievement.
But Finland bucks this trend, with high results and the lowest amount of homework, and there is also a very narrow social gap in Finland.
South Korea, another top performer in international tests, also has low levels of homework.
The research, which includes regional school systems as well as countries, suggests that Shanghai has the longest homework hours, followed by Russia and Singapore.
Italy, Ireland and Poland had high levels of homework for European countries, ahead of the UK.
But the UK's teenagers are studying longer at home than in countries such as Japan, Norway, Austria, Sweden, South Korea, Austria, Denmark and Switzerland, according to the research.
Among middle-class UK teenagers, the homework burden is disproportionately greater and above the average for both European and Asian countries, it suggests.
If late-night, last-minute homework seems familiar to parents, the number of hours might seem rather modest. The weekly average for the UK was about five hours - but, the OECD said, this was because the figures included young people who appeared to do almost no homework at all.
The gap between the homework hours of rich and poor could be about a lack of space to study, said Mr Schleicher. It could also reflect the amount of help that parents could give.
Mr Schleicher said schools could help to bridge the gap by providing a space in school where pupils could do their homework.
There could also be advice for parents to help them "motivate their children to finish their homework".
"The homework still has to get done, but maybe students and their parents will find it a little less troublesome," he said.
Brian Lightman, leader of the ASCL head teachers' union, said homework can have a "powerful impact on attainment" and that most secondary schools offer facilities where pupils can study after school or homework clubs.
"It is nevertheless important that children also have spare time for themselves. There is a risk that exam pressure can lead to excessive time spent on homework thus undermining opportunities for young people to develop character, skills and qualities to be successful in later life."
But parents, including those with younger children, might also think about their own extra homework hours, not to mention the arguments.
Cathy Ranson, editor-in-chief of the Netmums parenting website, said the study challenged the "common misconception that British kids are lazy and aren't being pushed hard enough".
"However, what the study doesn't show is that much of that homework is being done by parents not by children.
"With coursework counting towards some exam grades, some parents feel this is a way to push their child's results higher, while others believe their homework help will work like home tutoring."
She said that this was such a problem in some schools that at parents' evenings they were trying to "weed out mums and dads doing the homework".
"Teachers rightly point out children won't learn anything by relying on others if parents continue to do homework."