The Government has suggested bringing back the census date from January to September, when the academic year starts. The advantage of such a change is that schools should get more reliable budgets from local authorities.
They plan the amount of money they give to schools by April 1, the start of the local government financial year. The January census data comes back too late, so they have to rely on rough estimates of pupil numbers. As a result, they sometimes have to change schools' budgets in the summer if actual pupil numbers turn out to be different.
The drawback to the date change is that some authorities could get less money from the Government because most still admit children to reception classes at two occasions during the school year - September and January - meaning there are fewer children at school in the September.
It could also accelerate the trend for pupils to start school ever younger.
Mick Brookes, the general secretary of the National Association of Head Teachers, said: "This may well influence when children are admitted to school.
"It will be funding that calls the tune for schools because of the need to get children in, rather than other reasons such as whether they are ready to come to school.
"The proposal does need to be looked into to make sure it works for young children."
A study of 66 authorities, by The TES last month, found that a fear of missing out on funding was one reason that April admissions are now available in fewer than one in 10 authorities. Children increasingly start school in September of the school year they turn five, regardless of their birthday.
Authorities are already allowed to adjust the way they fund schools to reflect the fact that some pupils are due to start in April. But the Department for Education and Skills admits that many authorities do not use this flexibility.