Well, I went ahead and did it. The Battle of the Sexes classes have been officially reorganized. The numbers in my two after-lunch classes are now 9 boys and 7 girls and 8 boys and 8 girls. Has the gender balance been a magic bullet? No. Some personalities still stand out, but in general? The students seemed less playful and less social and therefore more focused on the task at hand.
This particular success could be my imagination, but grouping, in the form of class scheduling, small group work, and even seating assignments is a time-honored tool of classroom management. Even so, I believe we should use our power carefully. These days, we try to spin it positively to the kids, especially when we split up friends, as in you don't work very well with that person, and We just want you to be successful, and Don't worry! You'll still see so-and-so at lunch.
We do that because kids, especially middle school kids, often have a hard time with what we adults see as a simple schedule change. As an example, when I told my classes of the above mentioned switches, there were gasps and groans of horror, and many kids openly begged me not to change their schedule. This after four weeks of school.
I believe that there are far more insidious reasons for us to take care about moving students for their own good as well as the good of the class, though. In my experience, a lot of the time the kids we want to separate are minority students. In a diverse school such as ours with almost equal representation of Asian, Black, Latino, and White students, it's most often those Black and Latino cliques that get busted up in the name of group dynamics, and that gives me pause.