text: I'm not sure. There hasn't been any court cases involving private schools (even the on-going OGOD case is only involving public schools). In America the standard is that the full constitution applies if you accept any tax-money. 
  In South Africa the constitution is different though - it prohibits discrimination by private entities as well as public entities and requires private entities to not intrude on constitutional rights same as public ones.
  So it's possible that the court would find that a private Christian school must allow non-Christian students to join, and respect their religious differences. On the other hand the court has shown a deference to religious beliefs in terms of discrimination before (which is why we don't force churches that oppose it to perform gay marriages) - so it may go the other way. It's a bit of an unknown right now, but I would guess they'd be left alone - if only because other groups have a stronger case against government schools if they can say TBC