Almost one in five of computers in second-level schools are over six years old, according to a new national audit of information technology (IT) in education.
The survey found that fee-paying schools in general had much greater computer resources than those in the State sector.
Many State schools at both primary and second-level were hugely dependent on fundraising for computer facilities.
Last night both the Irish National Teachers' Organisation (INTO) and the employers' group Ibec were sharply critical of Government under-investment in IT.
The report shows that, with a pupil to computer ratio of seven to one at post-primary level, Ireland has improved only marginally in the past three years, and is still behind the OECD average.
It says over 10,000 computers in primary schools are in need of upgrade or repair, and over 5,500 are beyond repair or use.
Some 29 per cent of computers in primary schools and 19 per cent in post-primary schools are over six years old.
Last night Hannah Grene of Ibec said the "figures are a disgrace".
"As a wealthy country that prides itself on being at the forefront of the knowledge economy, we should be offering our children the best possible education and the skills they need to succeed. Irish students are being placed at a significant disadvantage."
John Carr, general secretary of INTO, said the report "shows that Government failure to invest in this area is damaging Ireland's future".
He said last year only €2.3 million was spent on supporting schools for the purchase of IT equipment. "This is in contrast to the North, where a €100 million plan for schools' IT is being rolled out.
"Where schools have modern computer facilities they are the result of local fundraising or support from businesses. Government can take no credit for the increase in computers in schools because it has made a negligible investment.
"Primary schools have fundraised three times what Government has invested, according to this report," said Mr Carr.
