I agree with Owen. One should wear what they are comfortable with regardless of who is teaching. I have had coaching sessions with some of the top professionals in our field, and trust me, I dress to dance, I dress to work. No shirt and tie here. Sweats, running pants, t-shirts, the same goes with my partner. And we dance Standard, not Latin. But if the individual is inguiring about group lessons or even private lessons in a studio enviroment where there are other students and staff members present, then I can agree with Anonymous, a business casual look is fine.