my son's school is a local aided school. there are quite a few expat kids in the school, too. so, it's not just chinese & mixed kids.
there are 2 streams at the school, because it is a school designated for non-chinese speakers.
A stream is chinese. all subjects are taught in chinese, except english. the chinese class is conducted in putonghua.
B stream is English. all subjects are taught in english, except chinese.
because my son's in A stream, yes, his mathematics is in chinese (just got 100% on his exam!), but if he were in the B stream, it would be done in english.
assemblies etc are all in chinese, so even the B stream kids, get more exposure to cantonese than they would ever get in an international school.
best thing about the school????
$0/month fees!