Gillies, R.M.  (2003). The behaviors, interactions, and perceptions of junior high school students during small-group learning.  Journal of Educational Psychology, 95(1), p. 137-147.

This study examined over one hundred 8^th grade students from multiple schools while participating in structured or unstructured group work in heterogeneous achievement groups over three semesters.  Gillies focused on helping (both helping behavior and receiving help), task structure, and student perception.  Students were less cooperative in unstructured groups than structured ones, but students showed similar learning outcomes.  Students in structured group work also thought that group work was more fun and produced better quality work.

It would have been more interesting to have the structured and unstructured groups compared with competitive or control groups on these measures.  But that wasn’t the author’s intent or line of inquiry.  She wanted to look at whether there was a difference (looking at lots of measures) between structured and unstructured group learning experiences.  She found a couple.  Interestingly enough, although the interactions might be different the academic benefit was similar or the same.  Students may feel differently about their group experiences but they were still educational experiences either way.