THE country's 720 post-primary schools have lost 650 teachers at a time when student numbers rose by 3,800.
The teacher cuts at second-level translate into fewer subject choices for students and less time with guidance counsellors.
The figures were highlighted in statistics published by the Department of Education allowing comparisons between the 2011/12 and 2012/13 school year.
As at primary level, enrolments at second level are rising as a result of the population boom. This will ultimately begin feeding into the second-level system as those children get older. Last year, there were 362,847 pupils in second-level schools – a figure that is set to rise for at least a decade.
The 3,800 rise in pupil numbers should have resulted in an extra 200 full-time teachers but 434 full-time posts were lost, according to the Teachers Union of Ireland (TUI).
TUI president Gerard Craughwell said: "Schools will simply not be able to offer students the same level of choice and subjects such as physics, music and languages, to name but a few, could be lost in some schools."
The deputy general secretary of the Association of Secondary Teachers Ireland (ASTI) Diarmuid de Paor said what was happening in schools was the very antithesis of what was needed for a functioning modern economy.
Meanwhile, parents, teachers, principals and school managers have joined forces to fight against cuts.
Their campaign will see every TD in the country receiving postcards urging them to join the resistance.
A new grouping, the National Alliance for Primary Education, is calling on the government to "leave primary education alone".
With the Budget date set for mid-October and Education Minister Ruairi Quinn seeking up to €107m in cuts, the postcard campaign will start this week.
Postcards will be sent to schools, and families of primary school children will be asked to send the postcards to all their TDs.
National Parents Council (Primary) chief executive Aine Lynch said the primary education system could not withstand any more cuts.
INTO president Brendan O'Sullivan said while ministers "talked up " the importance of education, only 9.4pc of public spending was devoted to it.
This compared with an average 13pc across the OECD.
Irish Primary Principals' Network president Brendan McCabe said among the cuts that the sector had suffered were reductions in grants to meet running costs, even though bills were rising.
Speaking on behalf of school managers, Paul Rowe of Educate Together, said children were the key asset for this country, but education cuts had direct and specific consequences on them.