The findings, by the Effective Provision of Pre-school Education project, challenges the orthodoxy that play is best for three and four-year-olds.
The team, led by Kathy Sylva, professor of educational psychology at Oxford University, said the key was getting the right balance.
She said: "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." Examples she gave included encouraging children to move on from scribbling to writing lists. It was not enough simply to let children pretend they were in a shop, she said.
They should have their play directed so that they were counting the money.
Researchers 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. Differences were found between good and adequate centres both in what and how the children 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.
Professor Sylva said: "You could say it's awful that children (in high quality centres) do less pretend play, but how much is enough? Though I'd hate it to disappear."
Researchers found the best centres put more emphasis on teachers spending time talking to pupils with an educational purpose, something that previous research has associated with poor nurseries.
Staff in the best nurseries would also teach informally by joining children's games in order to introduce ideas. Teachers in the low quality nurseries tended to formally instruct large groups. In adequate nurseries, teachers provided educational activities but spent more time monitoring play than getting involved. Conversations with children would not be as focused on learning.
The project began in 1997 and followed 3,000 children through 141 centres aged from three to seven. It concluded that the benefits of attending pre-school lasted until 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, March 2007