Discussion Groups/Equivalent?

I really like McGill, but I’m a little concerned about the size of the intro classes (for reference, I’ve been accepted into both the Faculty of Arts and the Faculty of Sciences, but if I go I’ll probably pick sciences). Do they break down into discussion groups lead by TA’s, or are students expected to learn from the lectures alone?

Large lecture classes do have discussion/lab sections just like at any large university in Canada and the US.