Research shows that students who work well together in groups are better prepared for the workforce.  As a matter of fact, that is one of the things businesses ask of schools.  In math, I have discovered that students who can listen, think critically and communicate their ideas clearly are more successful when it comes time for testing.  Short answer and extended response questions require students to have a deeper understanding of the material and they gain that from discussions with their peers.  I often tell my students that the difference between being proficient and being advanced or accelerated is being able to justify or prove their answer so that someone else can understand it.  Group discussion is so important.  Students who take on a leadership role in the group improve their own understanding and test scores.  This also helps the struggling students because they get positive role models of the thinking process which increases their test scores as well.  This is a great advantage because there is one of me and 28 or so of them.  I cannot be with each group all of the time.  I travel between groups and can spend a few minutes with each group, more time with a single group if needed.