This is an activity I use to review parallel lines in my high school Geometry class. It works best with 16 to 24 students, but can be adjusted to acomodate larger classes.
Each review portion has a particular suit attached to it. For example, finding slope and determining whether lines are parallel, perpendicular, or neither is the Diamond Portion. Determining angle measures that are congruent or supplementary based on two parallel lines cut by a transversal is the Club portion, etc.
Depending on the number of students, each person is given a playing card, Ace through four, or Ace through five, or Ace through six of each suit. I usually tie the card they are given to the section that they REALLY need to work on that day. Of course, there may not be exactly 16 or 20 or 24 students in the class, but that's OK. Some groups will just have one extra or one fewer person in it.
Then all the students with the same suit get together in a group, called the "Expert" group. They work on their particular section together, helping each other, etc. until time is called (usually 30 to 45 minutes, depending on the needs of the students). These students are the "Experts" in the topic they just completed. They also get name tags that say they are an expert in a particular topic, which is important for the second half of the activity.
After time is called, the students form new groups based on the rank of the card given to them earlier. So all of the Aces get together, all of the 2s get together, all the 3s, etc. These new groups are called, "Scholar" groups, and each one should have at least four members. Some groups might have 5 members, if the number of students is not divisible by 4, but that's OK. Now each group has at least one "Expert" for each worksheet. Each member of this group completes all of the other worksheets, and they help each other as they go along. This group also takes 30 to 45 minutes, depending on the students' abilities.
My students have benefited from this activity because they really enjoy teaching their peers, and some students learn better from other students, rather than always hearing it from the teacher. The students also like being an "Expert" and wearing a name tag that says so! I hope your students enjoy this activity as well. I always welcome feedback!