After-school clubs that are run by teachers or classroom assistants could force pupils to work the equivalent of a 50-hour week.
Christopher Arnold, senior education psychologist for Sandwell council, says that even well-run breakfast and after-school clubs often offer little more than an extension to the school day. As a result, children's school hours are longer than a 48-hour adult working week.
Dr Arnold found that, where the club is run by classroom assistants, most pupils say that it bears a greater resemblance to school than to home. But where clubs are run by external staff, a far larger number of pupils connect it to home life.
Dr Arnold conducted his study by observing wrap-around services provided in 15 primary and secondary schools in Sandwell, West Midlands. He presented his findings at the British Psychological Society's education conference, in Bournemouth this week.
"Where clubs are run by classroom assistants, children are more likely to associate them with things they do in the classroom," he said. "You expect adults at school to direct your work, decide where you sit. Where clubs are run by a third party, children associate them with things they do at home.
They decide what they do. This ability to make their own choices needs to be built into these clubs."
Some children at clubs run by classroom assistants told Dr Arnold that staff shout at them, and dictate their activities. Others said that activities are not directed at all, and that pupils are expected merely to do their homework.
By contrast, an eight-year-old in a club run by an external agency said that staff were "funny, and they help you".
A nine-year-old girl said that, if she were to run her own club, it would be the same as the one she attended.
But even these clubs have their limitations. A six-year-old boy told Dr Arnold: "Yes, I like coming. But I wouldn't like to come too much."
The Government recently announced its plans for schools to offer extended services, from 8am to 6pm. It aims for 50 per cent of schools to offer this by 2008, and all schools by 2010.