Is there academic research that supports individual over group work for better learning? I'm in an undegraduate program in the US where group work is a major focus in most classes. Faculty often cite the important benefits of knowing how to collaborate in teams, claiming how educational research findings strongly support collaborative learning.

I'm also a TA in a course in the department, and in our learning course, we had sections in which we strongly focused on the pitfalls of group work and how to improve the learning process (e.g. strategies to divide work, how to moderate conflict, with people who don't pull their weight, etc.). We were assigned a few papers on research about collaborative work (some even written by faculty in the department).

In all these papers, there always seem to be a behavioral assumption that makes the situation utopic. For instance, among the good strategies in papers were things such as: "Divide work early into task groups" or "Create a time estimate for the semester for every task." This is good advice, but not all students follow or care about these strategies. Otherwise, everybody would be getting As, no? Thus, despite my qualms about how the research was conducted, it seems that theoretically group work would be ideal, but in practice it is more often than not negative. 

Is there any research that has found that group work has more often been negative in academic settings? Or, perhaps, given the constraints (i.e. group is assigned, members don't know each other) or types of behavior (i.e. member who doesn't care about grade as long it's above C, member who just drops class) that exist in university classrooms, is positive group work unrealistic?

Additional related questions:


If there exists research that supports individual learning. Why is group work still insisted on? From the point of view of the professor, wouldn't it be preferable to assign a project (and if individual/group work is not a concern), let students organically generate their groups if they desire to do so, or work individually if they are willing to undertake the task alone?
If there isn't research that supports individual learning. What are some of the most important papers which have established group work as the desired learning strategy? Are there any popular experiments in the field of education related to this topic (e.g. famous/popular such as Zimbardo's experiments in Psychology)?
I found this study, which is a pretty interesting read: http://www.sas.upenn.edu/~jbryson/CBRReport.pdf
In the end it is proved that group work isn't beneficial. Most of the students who worked by them selves scored higher than the groups, by showing and explaining there work, but a bunch of others got the question wrong. The groups were scattered in the middle scores, meaning that they got more answers right than the individuals, but the individuals had a better understanding on how to solve the problem. When students work in groups, they get more questions right, but they don't understand what they are learning. This proves that it is better to work as individuals, since more students will understand what they are doing, although more will get lower scores. Also, the groups, probably only got more correct, since the students are collaborating and helping each other, which doesn't show that they understand what they are doing.