More than half of primary school pupils in the Shannonside Northern Sound region are in overcrowded classrooms.
Ireland has the most overcrowded primary classrooms in the EU, with more than 335,000 pupils in classes of 25 or more, according to the latest Department of Education figures for the 2019/20 school year.
According to the OECD, the EU average for primary class sizes is 20, but more than 60% of pupils in Irish primary schools are in classrooms of 25 or more.
Almost half of primary school pupils in Cavan, 49.4%, are in classrooms of 25 or more.
Longford comes next, with 50.4% of pupils in overcrowded classrooms.
However, around six in 10 primary school pupils are in overcrowded classes in Roscommon and Monaghan - 58.1% in Roscommon and 60.2% in Monaghan.
Meanwhile, 61.7% of primary school pupils in Leitrim are in overcrowded classes of 25 or more.
INTO General Secretary, John Boyle, said the "spectre of overcrowded classrooms looms large" over efforts for the "safe and orderly re-opening of schools" at the end of the month.