Thousands of low income, working families have been refused the back-to-school clothing and footwear allowance because they fall outside the payment's income threshold.
Some families have been rejected because they are just €5 over the threshold.
To qualify, a family's total income must be below a certain amount but the strict means-tested rules do not take into account expenses such as rent or mortgage costs.
Chief Executive of Barnardos Fergus Finlay says it will have a very bad effect on some children.
He said: "It costs about €300 to start a child in primary school and about €700 to start a child in secondary school, and there are thousands of families who are at the pin of their collar to afford this.
"One of the things we called for was for the income thresholds to be raised to enable enough familes to be able to afford what is supposed to be free education."
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