A local TD has expressed concern at new Department Of Education figures that show class sizes have up to 39 pupils in some parts of Wicklow.
Of the over 3,000 primary schools across the country, almost 20 per cent are in overcrowded classrooms.
The OECD estimates the average class size in most developed countries is 21.
However, two schools in Galway and one in Donegal were teaching pupils in record class sizes of 42.
Deputy John Brady has called on government officials to address the issue ahead of the return of schools in three weeks time.