But unfortunately there are no definitive answers in the research literature, according to Caroline Sharp, an early-years specialist at the National Foundation for Educational Research. "International comparisons are indirect evidence at best, because they involve such different cultures and educational systems," she says in a paper presented at the NFER's annual meeting last week. "What we can say is that a later start appears not to be a disadvantage to children's progress, although it is important not to forget the contribution made by children's experiences at home and in pre-school."
The most that can be claimed, she says, is that there appears to be no compelling educational rationale for fixing five as the starting age or for admitting four-year-olds to reception classes.
However, researchers have reached some consensus on the types of experiences that benefit young children. "Children aged five and under seem to do best when they have opportunities to socialise, make their own choices and take responsibility for their own learning," she says. "It appears possible for pre-schools to instil resilience and a 'can do' attitude, which serves children, especially those from disadvantaged backgrounds, well all their lives."
Research shows that emphasis on spoken language and on basic concepts such as time and number pays dividends. Providing access to books and story reading sessions is also important but "formal", academic teaching is not recommended.
Ms Sharp also points out that the debate over starting age is as old as the state education system. The 1870 Education Act stipulated that the term after a child's fifth birthday should be the starting age, but even in those days some MPs believed that six would be a more appropriate age.
Historical research by Martin Woodhead had shown that the earlier starting date had been justified on the grounds that children needed protection from "exploitation at home and unhealthy conditions in the streets". But the politicians also wanted to appease employers. Setting an early starting age meant that children could also enter the workforce earlier.
"Age of starting school and the early-years curriculum," by Caroline Sharp, NFER. Tel 01753 747281