An increasing population and more housing developments are said to be contributing to a shortage of school places in some parts of Wales.
A notice of motion to Cardiff council states there is an “imminent lack” of places and Pembrokeshire council said schools faced “increasing pressure”.
The National Association for Headteachers (NAHT) said ensuring enough places was “hugely challenging”.
Meanwhile, some other counties are seeing a surplus of places.
Cardiff council will discuss school places on Thursday with the notice of motion put forward by Liberal Democrat councillor Rhys Taylor which notes:
- Pupil numbers (from nursery to the end of primary school age) increased from 27,789 in 2010 to 33,469 in January 2017
- Demand for English medium secondary school places will be exceeded by September 2019
- Demand for Welsh medium secondary school places will be exceeded by September 2021
It also warned families with “economic means” were able to move within catchment areas to secure places at over-subscribed schools, leading to “a loss of community cohesion”.
Mr Taylor has called on the council to carry out a financial exercise and outline how it will deal “with the imminent lack of sufficient places in the city’s secondary schools”.
Cardiff council’s Labour group spokesman disputed the figures in the motion, describing them as “simply untrue” and “designed to cause panic amongst parents”.
“This is not the first time the Cardiff Lib Dems have tried to politicise school places,” he said.
“Education is too important to be a political football and it is irresponsible for the Lib Dems to suggest we are not actively addressing the issue,” he said.
Cardiff council said its 21st Century Schools programme was “designed to meet projected demand” for places.
It represents £164m of investment which is being used to build new schools and expand existing sites. There are currently two secondary schools under construction in Cardiff, along with four primaries.
A council spokesman said the next round of investment was being put to the Welsh Government and includes plans for three new secondary schools.
He added that new housing developments, such as the Plas Dwr development in north Cardiff, included new schools.
A spokesman from the NAHT said given the combination of full local school systems in parts of Wales, financial pressures facing local authorities and unanticipated mobility into the same area, “ensuring there are enough school places to meet the demand is hugely challenging”.
He said planning for places needed to be long-sighted and strategic, but it was a difficult proposition with “uncertainty surrounding public services delivery as a result of Westminster-driven austerity”.
“Every child needs to have an appropriate school place, preferably at their local school, and parents need greater certainty as early as possible in the process,” he said.
“School leaders frequently support their local authority within the admissions process, adopting flexibility where possible.
“We expect this approach to continue with the caveat that every decision keeps the needs of the pupils requiring admission, as well as those already in the school, front and centre.”
Pembrokeshire council said it has a number of schools where there is an “increasing pressure on places”, particularly at primary level.
A council spokesman said the authority has “particular issues in the towns of Haverfordwest and Milford Haven” and “it is likely this is as a result of increased population and housing development”.
He said the council had identified these two areas specifically in its planned 21st Century Schools programme which, if approved, will result in additional school places.
The Meads Infant and Nursery School in Milford Haven and Milford Haven Junior School will close next year to create a new school for pupils aged three to 11, a move the council said will help meet growing demand for places.
The schools under pressure in Haverfordwest include Prendergast and Fenton.
Other councils in Wales are facing the opposite problem – empty desks.
Several schools have shut and others are closing in Flintshire as part of the council’s modernisation programme.
Anglesey council began its £33m programme in 2012 to bring schools up to standard and address surplus places.
A council spokesman said: “Surplus places have reduced in the primary sector and are now at an acceptable level.”
The percentage of surplus places currently stands at 12%, with some primary schools being full or at full capacity.
“The council continues to review its modernisation programme proactively in order to reduce pressure on school places,” the spokesman added.