Young children do best in nurseries which spend less time on creativity and more time on academic subjects, research has found.
The findings, from the Effective Provision of Pre-school Education project, challenges the current orthodoxy that play is best for three and four year-olds.
The team, led by Professor Kathy Sylva of Oxford University, said the key was getting the right balance. "We hope this is not misunderstood as a defence of formal teaching. It is not. It is a defence of making a deliberate effort to encourage academic skills through play," she said.
Examples she gave included encouraging children to move on from scribbling to using pencils to write lists.
It was not enough simply to let children pretend they were in a shop or a doctor's surgery, she said. They had to have their play directed so that they were counting the money.
Myra Reid, quality improvement officer at East Renfrewshire Council, said schools in Scotland were now focusing more on "playful learning" - or, as it is described in A Curriculum for Excellence, "well-planned, purposeful play".
Thus, teachers and early years workers had to understand the purpose of children playing at a water tray or with sand, although she conceded that this was not always easy for staff to carry out.
Professor Aline-Wendy Dunlop of Strathclyde University said there was still "a long road to go in developing people's understanding of purposeful play and play in which good cognitive development could take place".
"I think we are in danger of putting in this thing called structured play, or creating a playroom. If play is a good thing for children and they develop well with it, we have to put the curriculum into play, not have play as an add-on to the curriculum," she said.
Researchers at EPPE analysed children's activities in 10 centres. Each centre was rated good or adequate against a 15-point system designed to assess the quality of the curriculum. There were differences between good and adequate centres in what the children were taught and how they were taught.
Children in good quality pre-schools spent significantly more time on reading and writing activities (14 per cent) than adequate centres (9 per cent). Adequate centres spent more time on creative play.
The researchers also found that the best centres put more emphasis on teachers spending time talking to pupils with an educational purpose, something which previous research has associated with poor nurseries.
But staff in the best nurseries would also teach informally by joining in with children's games in order to introduce ideas, while teachers in the low-quality nurseries tended to instruct large groups of children formally.
The Effective Provision of Pre-school Education project began in 1997 and followed 3,000 children through 141 centres from age three to seven. It concluded that the benefits of attending pre-school lasted until age seven. The project has now been extended to 2008.
* "Curricular quality and day-to-day learning activities in pre-school", International Journal of Early Years Education, vol 15, no 1, March 2007