Are study groups worth it?
Yes, if everyone shows up prepared and you actually quiz and explain things to each other. Asking each other questions and teaching a topic out loud are some of the best ways to learn, and research backs that up. No, if it turns into a hangout where one person talks and the rest copy notes. Then you'd learn more on your own.
The thing that makes a study group work is not the group. It's the quizzing and explaining. When you explain a topic to someone, you find the holes in your own understanding fast. When someone quizzes you, you have to pull the answer out of your head instead of just rereading it. Both of those are proven to stick better than skimming notes alone.
But a group only helps if everyone did the reading first. If half the people show up cold, the prepared ones end up teaching a free lecture and learning nothing new. Groups also drift. You start on cell biology and twenty minutes later you're talking about the weekend. Three people max, a clear topic, and a hard end time keep it honest.
So the honest answer is: a good study group beats studying alone, and a bad one is worse than studying alone. The deciding factor is whether people come ready to work. If they don't, study solo and save the time.