The issue is that tuition centres are money making entities.
Tuition centres claim that their methods are helping students with their school work and scores, which is alright if they just accept anyone and if almost everyone's grades improve
But when tuition centress accept only the best and claim that their methods produce the 90RP students, better than what MOE schools can do, something is wrong.
Amongst MOE schools, and it is not something unspoken ie it is widely mentioned, the good schools are only good because it accepts the best students. Other schools that do not accept the best students, the value add is easily observed here.