It would cost the Government €185 per child per year to deliver free primary education, according to the children's charity Barnardos.
The money would pay for school books, uniforms, well-equipped classrooms and free transport for those availing of the school scheme, the charity says.
It would also remove the need for parents to pay voluntary contributions and would ensure that schools had enough funds to meet running costs.
Barnardos has put the overall cost to the Exchequer at €100m per year, as it launched a campaign for free primary education.
According to the charity, the State pays €470.5m per year towards the cost of primary and post-primary schooling. An extra €103m per year would make primary education free and a further €127m would do the same at second-level, it claims.
Barnardos said the Government had a constitutional obligation to make primary education free for all children.
Barnardos CEO Fergus Finlay said the evidence from its annual school costs survey, which has been running for a decade, "clearly contradicts the persistent myth that Ireland has free education".
He said that fulfilling children's right to free primary education was "the constitutional responsibility of the Government and one they have shirked for too long. A right is not a right if you have to pay for it."
Mr Finlay described the investment required - €185 per pupil per year - as minuscule, but said the benefit to children and society would be immense.
"It's a question of prioritising resources to get maximum effect. The first budget of the new Partnership Government will be published this autumn as Ireland firmly emerges from a bitter recession which has left one in nine children living in consistent poverty. Now is the time for this Government to take a bold move and make free primary education a reality," said Mr Finlay.
Barnardos Head of Advocacy June Tinsley said the practice in Northern Ireland and other UK jurisdictions showed how to implement a truly free primary education system and "what is needed now is the political leadership to make it happen".
She said it was 50 years since then Minister for Education Donogh O'Malley announced the introduction of free education up to post-primary level.