I'm quite sure a school must support a student if they have adequate resources and enough people to run it. Eight people is definately enough to run a class.
Enough resources also means being able to cover the mandatory classes that have to be covered elsewhere in the school. Don't forget that all junior years have 50 hours of mandatory which have to be covered and then the classes moving into Year 12 have to be covered. It could come down to choosing between running an extension class for 8 students or a Year 11 class for 25 - so the Year 11 class runs but the extension class doesn't.