Children at five schools in Windsor and Maidenhead could be facing larger class sizes from next year.
The Berkshire council wants to increase primary and first school places by 15 per year group.
The plan would be implemented by September 2011 to meet the "significant rising demand" for places in the borough due to the rising birth rate.
The council predicts there will be 300 more children of reception class age in the area in 2013 compared to 2006.
The schools being considered for expansion are St Edmund Campion Catholic Primary and Holyport CofE Primary in Maidenhead, which would each increase places from 45 to 60.
Oakfield First in Windsor would change from 45 to 60 places.
Either Wraysbury Primary or Datchet St Mary's CofE Primary would also increase by 15 places.
The plans will be discussed at a meeting on Thursday and, if agreed, a consultation will be held, the Royal Borough of Windsor and Maidenhead said.
Councillor Eileen Quick explained: "The numbers of children attending first and primary schools are set to rise over the next few years and the council needs to act now to make sure we have enough places to cope.
"Increasing the admission numbers at these schools will allow us to offer local places to local children.
"Without expansion it is highly likely that some children living in the borough would not have primary school places here in September next year.
"We have looked closely at where demand is expected to be highest and at schools where sites are suitable for building expansion in time for next September."