Over 3,200 Kerry primary school students are in classes of over 30 pupils.
Figures published in the Irish Independent from the Department of Education show one-in-five Kerry pupils are in overcrowded classrooms.
Nationally, 130,000 children are in overcrowded classes, representing one-in-every four pupils.
Even with an average of 25, Irish classes are the second largest in the EU, where the average stands at 21.
Peter Mullan, Media Officer with the INTO, says class sizes should be a national priority.