Kinda surprised by this. SJKC grads I know/have met tend to have better command of BM compared to English.

Anyway, if they failed BM at UPSR then they are required to attend Peralihan right? If they passed, their level of BM might not be good but still able to communicate with others. If after all these and they can't even string together a broken sentence, then it's not an issue of whether they refused to learn BM but rather if they are capable of learning any subjects at all. Basically scraping the bottom of the barrel kind of situation.