I'm a twin mom, too. And although my boys have never wanted to be in the same classroom, if they did, I would fight tooth and nail to make it happen, if I thought it would be good for them. So, I think you're doing the right thing to try to keep them together.
Our school also separates twins, but it's state law that the parents get to decide whether to keep them together. What is your state law? What's your district's written policy? Maybe you can get some help there.
This article sites the rare research studies on this, plus gives a name of someone who regularly writes letters to support parents of twins who want to keep them together. Maybe that would help?
http://www.nytimes.com/2006/02/24/national/24twins.html?pagewanted=all&_r=0As for the teacher fit issue-- I wouldn't hesitate to be blunt about the reasons for requesting a move: You see your other son thriving, and while you realize the teacher has some good qualities, it's just not a good fit for your son's temperament. I think you could expand on the comparison between the two's performance and after school behavior. To me, this isn't an issue of whether you're hurting the teacher's feelings, it's of making sure your son is in the right environment to thrive, just as his brother is thriving. And I would stress it's not personal, when trying to make the move.
On the other hand, is it possible the situation could work out? We considered moving our 6 yo daughter (not a twin) out of a highly gifted class last year because she and her teacher were a poor fit. My dd told me the teacher was stifling her creativity! The teacher was strict, quiet, not artsy-- basically everything my daughter is not. But we knew the teacher because one of my twins had her (it was a great fit for him), and she's an award-winning teacher for gifted kids. We decided to stick it out and provide creative outlets at home. My dd has the teacher again this year (it's a 1st & 2nd grade class) and it works beautifully this year-- my dd just needed to mature in order to "appreciate" this teacher's high expectations. With feedback, the teacher has also gone out of her way to try to give my dd opportunities to be creative.
Good luck!
