You’ve just finished explaining a complicated concept to a group of 30 students. Based on your ability to discern understanding from the looks on their faces, you can tell that 8 students totally get it, 12 students are still wrestling with it, and 6 students look terrified, and 4 students are so overwhelmed that they’re on the verge of giving up.
Do you move on and keep the 8 students who get it engaged? Do you offer some practice to help the 12 students who almost get it? Do you back up a little to give the 6 terrified students another shot? Do you start from founding principles to give the 4 overwhelmed students a chance to get back on track?
All of these solutions require a teacher-led activity that targets one group of students, and doesn’t do much for the others in the best of cases, and might actually inflict damage in the worst.
Letting them choose means that many students will choose less-helpful friends over more-helpful strangers. Manually assigning them to groups based on a quiz would take much more that 15 minutes, and that assumes that you have a quiz ready, which you probably don’t.
Students indicate their self-assessed level of understanding, and Whudent quickly places them into groups by ability level. Once the students are in their groups, your role is to teach them how to learn together--how to offer and receive help--and not to restate the content.