At the moment, children who turn four between May 1 and August 31 do not get any time in reception class and are admitted straight into Year 1 the following September after they have turned five.
Education officer Andrew Wingard said: "All authorities face the same problem about how to prevent discrimination against summer-born children that can have lasting effects on their achievement."
If the changes go ahead, many private and voluntary-sector providers of nursery places for three and four-year-olds could be threatened with closure as their market share is reduced. And parents who might not think their children are ready to start reception class when they have just turned four may feel forced to take that option to ensure they get a place in a primary school.
Judy O'Connor, head of Charnwood primary, which admits children aged three into the nursery, said: "Taking all our children full-time at the age of four will mean we will be able to take fewer younger children as there will be much less space. We will have to undergo a major reorganisation."
Mrs O'Connor said four-year-olds were not too young for school as long as teaching was suited to their needs.
"The foundation stage does address this. There is plenty of structured play for our four-year-olds."
The council's consultation found that 62 per cent were in favour of children starting school at four. Supporters of the change say this will make the school admission system fairer.
Most of Leicester's four-year-olds are in school nursery classes or reception classes.
If the changes go ahead, they could be introduced in September 2003. Some authorities have early admissions into reception, taking all children in one go in September. Other schools still operate the traditional three-term entry.