Would you view this as favoritism? I have one class where most of the girls work well together, and stay on task, so I generally seat them next to their friends since they work well with their friends and stay focused. On the other hand, many of the boys in that class get engaged in loud, off-task conversations and don't do much work when I put them by their friends. As such, I keep the girls by their friends, but (with some exceptions) not these boys. I don't view it as favoritism as I have many classes where all the students work well so I try to put them all next to people who they work well with, but I don't want them to think I favor girls over boys.