It's so weird, the narrative from Labour has been so much about how this tax is correcting an unfairness that I think some people actually believe that the government subsidises private education 
@cansu : the government does not in any way subsidise private education.
The change they're proposing is to add an extra sales tax (VAT).
The whole cost of private education - and now also this extra tax - comes out of the parents net salary, ie after normal income tax has already been taken off.
Private health care, and private dentists, and private piano lessons are funded and taxed exactly the same as how private schools are currently funded and taxed. Ie No government subsidy. And no sales tax (VAT).
Do you have use a private dentist @cansu? Do your DC have piano lessons or swimming lessons?
Think whether you would see it as fair to have 20% extra put on top of your dentist bills or your DCs sports and music - just because people who don't have those things are pissed off that you have something (because you've paid for it) that they don't.
Does it make our society better that no-one learns music, just because everyone can't?