I don't teach him and I don't understand how he does it, but he's taught himself.
This struck me b/c this is EXACTLY how it is/was in our house. People would say "what did YOU do to him", and I would reply, "if I did anything, you'd see me on TV, as I would be a millionaire because of my teaching methods".
DS7 (well, 7 on Saturday) was able to play fine with all kids, and he still is. He was more advanced academically, but it never became an issue until an adult made it such. I wanted DS moved up, but in the end, it didn't matter where he was. He enjoyed it.
Your DS is enjoying his time. So, I wouldn't necessarily ask to have him moved. BUT, I would say something to the director. 1, the teacher has NO right to tell you what to do with him outside the classroom. And 2, as a teacher, it is her JOB to answer the questions asked by the students. If she doesn't like the differences in her kids, then she needs a new job!
Kids, like adults, come in all sorts of shapes, colors and intelligence levels. And a good teacher, especially for that young of a child, will adapt to her ENTIRE class's needs.