More than two in three private schools have increased their fees this year.
An increase in foreign students enrolling as a result of Brexit and the economic recovery are said to be contributing factors.
34 out of 51 private day schools increased their fees by between €100 and €200 this year.
Former headmaster of St Andrew's College, Arthur Godsil, says the reason is due to private schools being in competition with each other: "The reason why they're increasing their fees is because they will need to develop their premises.
"Whereas the State will pay for teachers, they don't pay for any buildings or any developments, so because we're in competition with each other, they do have to improve".
According to The Irish Independent, St. Columbia's college in Rathfarnham, Dublin is the most expensive private school with fees costing students €8,241 for a day pupil, followed by Sutton Park and Alexandra College.
Recent figures from the Department of Education show that it would cost the state around €24m to transfer private schools into the free education scheme.