To be encouraged not banned. The idea of closing down schools because they are performing better than other schools seems ridiculous. Rather than banning faith schools so all schools are on an even, but lower, playing field, a logical course of action would be to try and determine exactly what it was about faith schools that made them perform so well and attempt to emulate that in ordinary schools to improve their performance.  It may be possible to convert the schools but they would loose their ethos. Without these schools religious ethos their standards would slip and the students would be worse off.