The Society of St Vincent de Paul says it received up to 300 calls per day last week from worried parents struggling with back to school costs.
The charity says calls for help with the costs have increased for the third year in a row.
This summer saw a 4% increase, which follows a 20% increase last year.
According to the charity, the smaller figure this year suggests an increase in the Back to School Clothing and Footwear Allowance has helped reduce the pressure on families.
However, they say 'much greater investment' in the system to ensure costs aren't a barrier to children's participation.
The charity is calling for free school-books for all primary and secondary schools, and for the voluntary contribution system to be scrapped.
SVP's Tricia Kielthy said the housing crisis is making the problem worse.
She explained: "[People's] priority is firstly to keep a roof over their heads, so that means they may put bills on the long finger, or they may cut back on things like food... they may just not have enough to meet the cost of education at back to school time.
"These figures don't really capture families who contact SVP because they've cut back on food or electricity or gone into debt to cover back to school costs."
The charity's proposing a €20 million investment in Budget 2020 to provide free books to all primary school children.
They're also proposing a working group be set up to examine the use of digital devices in schools, including the cost impact it has on parents - suggesting equipment and software costs can be between €500 and €800.