Almost one in four primary school pupils are being taught in classrooms with more than 30 pupils.
The Department of Education's figures show that more than 124,000 pupils are in super-sized classrooms.
Figures from the Department of Education show that schools in the Dublin commuter belt are the most populated. Meanwhile, schools in less urbanised areas are experiencing lower enrolments, leading to an overall lower national average for class sizes.
The Irish Primary Principal's Network says large class sizes impede the ability of teachers to cater to individual childrens' learning abilities.
Brendan McCabe, President of the IPPN, told Newstalk's Breakfast pupils benefit more when teachers can give them more time:
The Irish Primary Principal's Network is concerned that figures released by the Department of Education on class sizes do not reflect reality.
The Department of Education say they have maintained the pupil teacher ratio this year, despite a growth of of 10,000 new pupils.
Minister Ruairí Quinn says a thousand more teachers were employed in 2014 to keep the pupil-teacher ratios steady.
