, is not surprised. "Children get extremely tired mentally and physically at school," she said.
"Then they have to come home and do more work on top of that. It's counter-productive.
"While we're making six-, seven- and eight-year-olds do extra work, in some countries they wouldn't even have started formal schooling."
The researchers said the effectiveness of homework also depends on what, and how much, is set. Many primary teachers set homework intended to improve time-management and organisational skills, rather than results.
But David Fann, head of Sherwood and Broughton primaries in Preston, Lancashire, insists homework does improve achievement.
"Reading books at home, or doing half-a-dozen spellings, is an essential part of primary education," he said.
"Without that process, a lot of children wouldn't have acquired confidence in their literacy and numeracy skills.
"It's a reinforcement of what's going on in school. And it also keeps parents informed, as well as breaking down the barrier between home and school."
Reference: `Does homework improve academic achievement?' by Harris Cooper, Jorgianne Civey Robinson and Erika A Pattall, Duke University