Private schools have asked the Government for more funding on top of the $10 million increase they got this year.
Independent Schools of New Zealand says this year's rise worth about $300 per child hasn't stopped a fall in enrolments.
The organisation says if those children go into the state sector, they cost the Government about five times what it pays for private education.
It argues it would be cheaper for the Government to increase its funding so private schools are more affordable.
That would also reduce the number of private schools seeking to join the state sector as integrated schools, it says.