An Orkney woman who wants independent schools stripped of their charitable status is taking her campaign to the Scottish Parliament.
Ashley Husband Powton believes the rules should change on allowing private institutions the reduced tax bill.
She will put her case to MSPs on the public petitions committee.
However, John Edward, who is director of the Scottish Council of Independent Schools, said the charity status test was a stringent one.
He explained that private schools received charitable status because they "deliver charitable purpose like 23,500 other charities in Scotland".
Mr Edward added: "And in their case their charitable purpose is the advancement of education and nobody questions the education they deliver and part of that is the test they are put through by the charity regulator to demonstrate what their purpose is."
Private schools serve about 4% of Scotland's pupils.
Because of their charitable status, such schools do not pay corporation tax and receive an 80% discount on their rates.
Campaigner Ms Husband Powton told BBC Radio Scotland's Good Morning Scotland programme: "Most elite private schools charge fees of more than £30,000 a year and the average wage in Scotland is about £26,000 a year, so that shows just how inaccessible these schools are for most people."
She added: "Private schools represent the very opposite of what a charity should be, that is an organisation that helps the needy and the most vulnerable in society and not already the richest and the most privileged.
"The provision of a few bursaries, and it really is a very negligible amount when you actually look at the figures, cannot be allowed to mitigate the overwhelming reality that for the majority of the population a private school education is far outwith their reach."
However, Mr Edward said that he knew "for a fact" that thousands of children would be going to school on means tested bursaries "right through to 100% of the bursary".
He added: "The charity regulator was very clear in testing the schools to not just the scale of provision for financial assistance but also making sure that those most in need were able to access the services of independent schools."