The council will maintain P1 classes at 25 pupils
Councillors in Falkirk have said they will struggle to achieve the Scottish Government's policy of cutting P1 to P3 classes to a maximum of 18 pupils.
The local authority warned it was only able to maintain class sizes of 25 pupils for children in primary one.
They have blamed their lack of progress on an above average rise in population and a lack of available funding.
The policy to reduce class sizes was a flagship manifesto pledge before the SNP's victory in the 2007 elections.
The council's education committee said where new primary schools or extensions were being built, they were designed for P1 to P3 classes of 18 pupils.
However, they said that there were no additional resources available to achieve the 18 target in other primaries in the area.
The committee also warned that pressure on school places will rise as a direct result of Falkirk's above average rise in births, up 6% last year.
The authority said that they were less able to raise cash for building new schools or extensions by selling surplus land because of the current financial climate.
Julia Swan, director of education services said: "Our birth rate is projected to continue rising until 2013 unlike some other areas in Scotland.
"Predicted demand for school places does not include the children of families moving into this area.
"We recognise the educational value of smaller class sizes but the present level of available resources limit the options we have."
Education Secretary Fiona Hyslop has indicated she will work with local authorities struggling to meet the targets to ensure progress was made.