One in five primary school students are being taught in overcrowded classrooms.
Almost half of primary schools have a classroom of 30 pupils or more.
While there's no set limit on primary school classroom sizes, the Department of Education recommends no more than 25 pupils per teacher. Almost 20 per cent of pupils are in classes which could be considered overcrowded.
The biggest class size in primary education was 42 and was recorded in two county Galway schools, Scoil Náisiunta Rois, Taylors Hill and Bunscoil Phadraig Naofa, Tuam.
Donegal’s NS in Cardonagh also recorded a class size of 42.
The county with the highest average was Meath, which has an average of 25.6 students per classroom.