Group projects, while occasionally useful in limited settings, are usually just easier for the teacher, not best for the student, despite all assertions to the contrary. They create less for the teacher to grade, and what is graded is highly subjective. The teacher also knows that SOMEONE in the group will make it happen, and this will allow the teacher to pass everyone, thus avoiding confrontations from students earning poor grades. However group projects are frustrating to those who do the work and have to put up with those who don't. By avoiding giving the grade deserved by each individual, because the teacher doesn't even know what each individual has done, it short changes the students who have not been productive. In fact it promotes the attitude of just sit back and let someone else do it, because someone WILL do it, and they'll all get the same grade anyway. It actually creates the same situation that causes communism to fail! Even the pilgrims of Massachusetts found that people work harder when they have their OWN property to take care of individually rather than collectively.
Grouping works best if it is very short-lived, not graded, and used mostly to discover or reveal some little thing, after which the lesson continues. There may be some limited success using group projects, but usually this is not the best way to teach or for students to learn.