MEETING HIS MOM TOMORROW?!?

i have been talking to this guy for a while and we decided to go out. he is supposed to be coming with me to my school's dance (we go to different schools). the only problem is that i have to meet his mom first. he says she is kind of mean and REALLY strict. she says his dates have to go to his school. i just transferred out of his school a couple of weeks ago. i am going to that schools choir concert tomorrow evening (he is in it) and after the show he is going to introduce me to his mother. how do i make sure she approves? what should i wear? also we are going out for ice cream in a small group after. that's not really relevant. how should i handle his mom???