Almost 27,200 students were enrolled in private post-primary schools in the 2022-2023 school year.
Clongowes Wood College near Clane is among the most expensive boarding schools in the country.
Socialist Party TD Mick Barry has called for an end to State funding for fee-paying private schools.
His call came in the wake of reports that the number of students attending fee-paying private schools last year (2022-23) was the highest on record.
The State is set to pay €112m to private schools in 2023.
Among boarding schools, St Columba’s was the most expensive for seven-day boarding (up to €25,904); followed by Clongowes Wood College, Co Kildare (€21,840); Rathdown School, Glenageary (€21,630) and Glenstal Abbey, Co Limerick (€20,475).
The highest fees in the state charged by a private school for day students are €8265 at Cistercian College, Roscrea, Co Tipperary (265 students).
The highest fees charged by a private school for day students in Cork are €4500 at Christian Brothers College (908 students).
Deputy Barry commented: "Private fee-paying schools can charge more than €20,000 a year for boarders and up to €8,000 a year for day students. By handing over €112 million to these schools this year the State is subsidising inequality.
"That subsidy should end. The State should continue to employ the teachers in these institutions but the institutions should be made to foot the bill in its entirety."

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