Over 11,705 primary school children in Cork are crammed into classes of 30 or more, according to figures released this week by the Dept of Education.
The statistical bulletin revealed that Irish primary school pupils are being educated in some of the most crowded classrooms in Europe.
The figures also showed that far more pupils in Co Cork suffer larger class sizes than their city counterparts. 63.9% of pupils in Co Cork sit in a classroom of 25 or more pupils (the tenth most drowded in the country) compared with 48.8% of their city cousins (the least in the country).
In Cork overall, 23.8 per cent of all pupils (or 11,705 school children) are currently being taught in classes of 30 or more.
On their return to school in September, 4-12-year-olds face classes with an average of 24.3 pupils, well ahead of the EU norm of 20 and an average 21 across the developed world.
The only EU country with larger primary classes is the UK.
Two in three primary pupils are in above-average size classes of 25 or more - second only to the UK in Europe.
Overall, 347,524 of 555,319 pupils enrolled in the school year just ended were in classes of 25 or more, according to data released by the Department of Education.
It includes 109,614 in 'supersized' classes of 30 or higher, with 288 of those in classes of 40 or more.
The figures represent an improvement on average class sizes of 24.9 in 2015/16, while the number of pupils in 'supersized' classes has also reduced, from about 125,000.
The Government is under pressure to tackle class size in the forthcoming Budget, but Education Minister Joe McHugh is non-committal. The Irish National Teachers' Organisation (INTO) has made it a key demand, sparking a raft of parliamentary questions to Mr McHugh.
A spokesperson for the minister said he had nothing to add to recent comments that any additional improvement would have to be considered alongside other demands from the sector.
A further one-point improvement in the pupil-teacher allocation ratio at primary level would cost about €135m a year.
INTO general secretary John Boyle said "class sizes are far too high".
"With only 11pc of Irish children learning in a class of fewer than 20 students, the EU average, it's clear they are being short-changed," he said.
He said smaller classes supported inclusion and diversity of children, and allowed for more individual attention.
He said younger children in particular benefited greatly from smaller classes.
Fianna Fáil education spokesperson Thomas Byrne said reductions in class size were part of the Confidence and Supply Agreement and, while he was delighted to see progress made on foot of Budget 2018, "we want to see more".
With school enrolments now peaking after about a decade of growth, Mr Byrne said the changing demographic provided an opportunity for more progress.
One priority for Fianna Fáil is schools in the DEIS scheme for disadvantaged areas, which have smaller classes - but an advantage that has narrowed after the general improvements in 2016 and 2018, when there was no corresponding reduction in their pupil-teacher ratio.