As a second grade teacher, I use a wide variety of strategies in my class. I think that originally "cooperative groups" or "learning" entailed having roles assigned to members (leader/facilatator, recorder, reporter, materials manager, domestic engineer, etc.) and having fairly orderly sets of behaviors and ativities required. I do believe that people need to be taught how to work together, I don't think it's entirely natural--although it has certainly been necessary to get us where we are today--alive! Anyway, I'm more comfortable with looser interactions for second graders. Partner and group work is almost always appropriate in our class. Children assume that unless I say otherwaise they are welcome to work with other children in our class. Most of these pairing or groupings are self-selected. However, everyone knows that no one is to be left out who wishes to work with a group (no one is forced to take on a partner, however, unless the activity dictates a partner.) I set up groups myself from time to time and chidren are seated in groups of four that I've arranged for a good heterogeneous mix--sometimes I require the children to work in these groups (I don't consider having your desks together working together, though). Anyway, what I've discovered is that when I occassionally use random seletion of groups those tend to work the best.
Since children are not REQUIRED to work in groups--except SOMETIMES-- those who feel the need to "move on" or go slower, or whatever, may choose to work alone on occasion. They may also present to the class alone. Since none of our acitivies or problems can be done or solved in only ONE WAY and since many of our problems have more than one correct answer it is easy for all of my children to be able to present and solve problems using techniques that work best with their thinking and their strengths. They also get to see how others think.
So, sometimes I assign groups based on my vast knowledge of my students and their needs and SOMETIMES I require everyone to work in these assigned groups, sometimes I DON'T require anyone to work in groups although it is perfectly permissible, and on RARE occasions I require that students work alone. And OFTEN I'm amazed that the groups that neither the children nor I select are the ones that work the very best. Oh, yes, SO M SOMETIMES I even put my more needy kids together--the ones who don't try or who don't speak during presentations. That way they're forced to come up with something! And because we VALUE mistakes in our class and treat each other with respect (and I don't mean this facetiously as I did my vast knowledge remark up there) even if the group gets it all wrong and confused they are not embarrassed or penalized, we just all learn from their mistakes! See? There is no ONE right way to do group learning! :-) Cindy