Parents have had to stop paying bills or cut back on daily essentials to fund back to school costs.
A Barnardos survey says parents are bearing the brunt of "an under-funded education system."
It found parents of primary school pupils pay on average between €50 and €100 on books - while 20% of parents of secondary school pupils pay over €300.
Parents also spend on average €95 on school-specific uniforms at primary level, and up to €200 for them at secondary level.
Barnardos says: "There remains a constant expectation that parents will prop up the educational system by having to buy the essentials required for their children to complete the curriculum i.e. books, classroom resources, stationery and voluntary contributions."