Do it. I did it last year, and was encouraged to do so by the teacher (she was actually the one who brought it up). At least at our school, having it on the form was helpful to them in making sure it happened. I felt a little bad about it, as I felt most parents would probably want to avoid the kid in question, and tried to phrase my reasons neutrally though I'm sure everyone could read between the lines. I think I wrote something like 'if possible, we would like Larlo separated from Marlo next year, as their interactions in class this year have been troublesome and are impacting Larlo's enthusiasm about school and ability to focus on learning'.