Almost one in five primary school children were in classes of 30 or more last year, with six schools recorded as having classrooms with 40 or more pupils.
An analysis of data published by the Department of Education on more than 22,700 mainstream classes in over 3,100 primary schools across the Republic show 19.8% of all pupils are in classes which could be considered overcrowded.
It reveals that 45% of all primary schools had at least one classroom of 30 pupils or more in the 2018/19 school year.
Despite large numbers of new teachers being recruited in recent years, many schools continue to experience difficulty in keeping class sizes at recommended levels.
Three schools had a record number of 42 students in a primary school classroom: they were Scoil Náisiúta Róis, Taylor’s Hill, Galway; Scoil Naomh Colmchille, Carndonagh, Co Donegal and Bunscoil Phádraig Naofa, Tuam, Co Galway. Meanwhile, Scoil Naisiunta Cillmin in Clonakilty, Co Cork, had 41 and Ballyhea NS in Charleville had 40.
The school with the highest average class size in the country was Scoil Mobhi in Glasnevin, Dublin where last year it had an average of 31.9 pupils in each of its eight classrooms.
Overall, more than 109,600 out of 553,319 registered primary pupils in the recent school year were in overcrowded classes.
Young schoolchildren in Kerry were most likely to be in overcrowded classrooms with almost a quarter of all pupils in the county in classes of 30 or more.
Other counties with above-average levels of pupils in very large classes were Limerick, Westmeath, Kilkenny and Carlow.
Three schools had just three pupils registered last year — St Columba’s on the Co Mayo island of Inishturk; Bofield National School in Bofield, Co Mayo; and the Educate Together National School in Fermoy, Co Cork.
The school with the largest class sizes in Cork is Scoil Chaitriona, Ballynoe, Mallow with average class sizes of 30.3 last year.
The figures show the number of students in classes of 25 or more across the country is over 347,500 —approximately 63% of the total.
However, the Department of Education figures also highlight how average class sizes nationally have been falling continuously since 2015/16 when they stood at 25.4 pupils per class.
The average class size decreased by at least one pupil per teacher in 925 schools last year but increased by at least one pupil per teacher in 753 schools.
According to the OECD the average class size in most developed countries is 21.
There is no statutory limit on the size of general classes, although a Department of Education circular in 1990 stated that “appropriate learning experience is difficult to achieve when classes consisting entirely of mainly four-year-old children exceeds 25”.
The department said the staffing schedule for the current school year at primary level was operating on a general average of 26 pupils for every teacher.
A spokesperson said the guidance issued to schools was to keep the number of pupils in any class “as low as possible”. It is estimated that lowering the primary staffing level by one student per teacher would cost approximately €135 million per annum.
While welcoming a reduction in class sizes in recent years the Irish National Teachers’ Organisation said they remained “far too high” and called for Irish levels to reach the EU average class size of 20.