A new study has found that the average cost of sending a first year student to secondary school is almost €800.
The Barnardos School Costs Survey shows parents of children starting primary school will have to spend an average of up to €400.
According to Barnardos, parents are feeling more financial pressure than ever before, with books, uniforms and voluntary contributions the main causes.
One of the biggest complaints among parents was the added expense of a school crest on a uniform.
In the survey, 56% of parents at second level and 48% of parents at primary level said they had applied for the back-to-school clothing and footwear allowance.
The allowance was cut by €50 in the last Budget to €100 for a primary school student and to €200 for a second level student.
The Department of Social Protection said the allowance is not intended to meet the full cost of returning to school and that the rates for this year compare favourably with advertised prices for back-to-school clothing and footwear.
But Barnardos Chief Executive Fergus Finlay has described the allowance cut as "scandalous", saying it was the biggest single cut made in that Budget.
He also said Minister for Education Ruairi Quinn should stop "asking" schools to take action on the cost of uniforms and schools books and should instead move to legislate on such costs.
Mr Finlay also said that despite the Department of Education's efforts to discourage so-called "voluntary contributions", there was "acres of anecdotal evidence" that parents continue to be asked by the children's schools to make these payments.
Speaking on RTÉ's Morning Ireland, he described these contributions as "discriminatory" and "intimidatory" and said that "they punish children who don't have it".
Around 1,100 people took part in Barnardos online survey.
Sinn Féin deputy leader Mary Lou McDonald called on the Mr Quinn to take a stronger line with boards of management to implement policies which allow parents the freedom to buy cheaper school uniforms.
"The message here is clear: austerity is not working. Citizens are under real pressure and this is the message that the government must heed when it is drawing up the October budget."