A quarter of secondary school parents said they had to take out a loan or borrow from friends in order to meet back to school costs this year.
Research from Barnardos shows the average cost of the basics needed for a 4th class pupil is €320 - this climbs to €972 for a student going into 1st year.
The cost of sending a 5th year pupil back to school stands at €863.
Half of primary and two-thirds of secondary school parents have said they are worried about meeting costs this year.
While one-third of primary school and half of secondary school parents said cost of living increases have made it much more difficult to meet costs.
Barnardos CEO Suzanne Connolly said the introduction of free schoolbooks for primary school students has made a difference.
"Last year, the Government took the welcome step of introducing free schoolbooks for all primary school children," she said.
"This year Barnardos is calling on the Government to continue this progress and extend free schoolbooks to all secondary school children to help to provide a genuinely free school system for all children.
"Barnardos believes that no parent should face financial pressure in trying to meet what are essential costs for their children’s education," she added.
The charity is also calling on all schools to provide a low-cost uniform option, and for an end to voluntary contributions.
Barnardos Back to School Survey, which was carried out in June and July, received over 1,140 responses.