Instead of asking the principal for 28 sets of fraction pieces, I ask for 7 sets, one for each group. This is a tremendous costs savings. Having one set of manipulatives per group reduces the time needed to put things away at the end of an activity. Students sometimes explain things to each other better than a teacher can to an entire class of students. This usually results in better retention of material.
Questions are more likely to be asked and answered in a group setting.
Students today seem to have a much shorter attention span than they did years ago. With cooperative learning used on regular basis, they are less likely to become restless or misbehave during a teacher-directed part of a lesson since they know they will have time in groups. Shy students are more likely to ask and answer questions in a group setting. The same is true of low-skills students. Today's job market is looking for people with good interpersonal and problem-solving.