The latest school costs survey by Barnardos has found it takes €785 to put a child through their first year of secondary school - an increase of €50.
The children's charity said the overall costs of sending a child to school have gone up this year compared with 2014.
It now costs €365 for a senior infant - up €20 euro - while it's up €10 to €390 for a child in 4th class.
The average price of books has increased by around €25 and voluntary contributions now average €150.
Books continue to be a substantial cost, particularly for secondary school pupils, where they make up on average over 40% of the total costs.
The survey also found voluntary contributions are up, while there are some savings to be made in the cost of uniforms and school shoes.
Fergus Finlay, the CEO of Barnardos, said "survey after survey has told us the true cost of Ireland’s supposedly ‘free’ education."
"It is very clear our education system is underfunded and under-resourced and there is an unfair expectation that parents will plug the gaps."
He said over the last 10 years in which the survey has been run, parents have consistently told of their difficulty in paying for back-to-school costs – including stories of avoiding paying bills, cutting food budgets, or borrowing heavily.