More than one in seven Junior Certificate students has special needs, learning difficulties or does not speak English as their mother tongue, according to new research.
The study, conducted on behalf of the Association of Secondary Teachers Ireland (ASTI), also found that 64 per cent of third-year students are taught in overcrowded classes of 25 students or more, with 16 per cent taught in classes of 30 students or more.
The ASTI estimates that this equates to more than 100,000 students being taught in classes of 25 or more, while more than 25,000 students are taught in classes of 30 or more.
Overall, it says this represents an increase on previous years.
However, Minister for Education Mary Hanafin yesterday said there have "never been more teachers or fewer students at second level than we have today.
There is actually a teacher for every 13 students in our second level schools and schools have a huge discretion in how they allocate those teachers," she said.
"You might have 25 in an English class but then you might only have 10 in a physics class . . . so each school can determine for themselves."
Ireland comes 29th out of 30 OECD countries in spending on second-level students relative to GDP per capita, John White, ASTI general secretary, said.
Large class sizes significantly affect the time which teachers can spend with individual students, many of whom come from increasingly diverse backgrounds due to the welcome "mainstreaming" of education, he added.
Fifteen per cent of classes had special needs students (7 per cent), students with learning difficulties (5 per cent), or students not having English as their mother tongue (3 per cent).
The ASTI called for 2,000 new teachers to put an end to classes of 30 or more as a first step.