Hard-pressed parents could find themselves having to spend up to €620 for each of their children going back to school next month.
Research found the average parent expects to pay around €487 for a child attending primary school and €620 for secondary school.
The National Consumer Agency has warned parents to budget for the costs, which include school uniforms, books, stationery, gym gear and school bags.
Chief executive Ann Fitzgerald said a family of four, with one primary and one secondary level child, could be forced to spend up to €1,100.
"Spending this amount of money on back-to-school costs is a significant financial pressure for most parents, especially those who may be already struggling financially," said Ms Fitzgerald.
"For parents who are worried about their back-to-school costs, working out a budget, planning their spending and looking for ways to cut their costs can make a big difference."
She said it was important for parents to budget.
The study, conducted by Amárach Research on behalf of the NCA, also found that 78% of parents are more concerned about the costs than they were last year.
More than half of those surveyed (59%) said they would use their regular income to cover the costs, 27% said they would put money aside, while a fifth had applied for a back-to-school allowance.
Some 15% of the 1,002 parents asked said they would have to dip into their savings, while 5% will be forced to pay with a credit card or overdraft.
The remainder will either have to borrow from friends or family, take out a personal loan or borrow from a money lender, while 1% said they did not know how they would cover the costs.
Ms Fitzgerald advised parents to look for bargains where they can because prices on school items can vary among retailers.
"We would also urge parents to not feel pressurised into buying the most expensive school items for their children, especially where these items may end up getting lost or only last a short period of time," she added.
"Parents can use money-saving tips to make sure they are not spending more than they need to and get the most for their money."
The NCA findings come on the back of a survey which found parents are cutting back on food and bills in an effort to cover the costs of sending their children to school.
Journalist: Lyndsey Telford