Primary schools 'on the breadline'
A union survey found that for every euro schools must spend on heating, lighting, insurance and other running costs, only 75c is provided by the Department of Education.
In some cases, schools are having to raise more than one-third of their annual budgets themselves, involving sums of up to €15,000.
The INTO, which carried out the study among 10 Dublin schools, has urged the department to fund schools properly so teachers and principals can get on with the job of teaching children.
The schools surveyed had a total of 3,000 pupils and running costs of €527,000, but only received €400,000 towards these costs from the Department of Education.
The department's capitation grant to each of the State's 3,200 primary schools is based on the number of pupils, with €133.58 given to school boards for every child enrolled. For every student in a second-level school, the Government pays €286.
Education Minister Mary Hanafin announced last month that this would increase by €12 per child next year for both primary and second-level schools, giving a 500-pupil school €72,790 up €6,000 on this year. The money goes towards running costs, including office expenses, classroom materials and cleaning bills.
But INTO general secretary John Carr said that even the increased grant will not be enough.
Based on its survey, there is an average shortfall of €44 per pupil on the 176 schools spend for each child.
"Most primary schools are on the breadline when it comes to funding but the gap between State funding and real spending is covered over by local fundraising," he said.
Mr Carr said schools could not operate without this additional income, although many parents often raised questions when asked for voluntary contributions or to attend fundraising events, as they expect the State to provide free primary education.
"They often fail to realise that schools are not raising money to get additional extras, but for the bare necessities. This is an unfair and unjust local education tax," he said.