I think it's important, if you're doing in-person study groups, that each student should have to answer questions in front of the rest of the class -- put them on the spot, both to wake them up and as an incentive to study so they don't look bad.

What's a good level of challenge for some would lead to paralyzing anxiety for others. One advantage to a mostly online system is that students can choose classes with policies that suit the way they learn.