They are then participating with another classmate while reviewing the material for themselves. I also do the quiz thing and they get quite into it. I've found that some students are excellent teachers. Also, each group is in charge of presenting the solution to at least one of the problems in the assignment. That way, the members are accountable to the group, that is, the group must make sure that each member of the group understands the material well enough to present it.
Accountability is very important to success.
But if learning is target, then it helps everyone. I believe in practicing by doing, however, my grading at the beginning is more relaxed than later in the term. I ask them to introduce themselves to each other. If learning happens, the grading takes care of itself. Next week we will be talking about How to get students to be responsible for their education.