Sometimes I think you and I are in opposing universes and reading your posts, especially about the preschool, makes me ponder if I over reacted to DD's time with her social preschool. I used the exact same argument about why it might be better for her since DD loves arts and crafts plus singing and dancing, etc. We also watched DD shorten her words to 3 word sentences max when the child has been able to speak in complicated sentences 15+ words before age 2. She could also write and draw but followed the kids' lead and just scribbled. I think you get the picture.
But to answer your question about the teacher. I thought the same thing ... don't tell them a thing. They will surely figure it out. DD wouldn't reveal that part of herself so they never saw it and when I told them later about her abilities the teacher was in shock, but by this time I had already decided the school was not a good fit and was looking to move her into another school. I know I really didn't give them a chance to try once they learned the information but the school we wanted to move her into had one spot open up and we had to take it by that week or we would lose it. A few months later DD and I ran into her old teacher while at a store and I was quite amused by the interaction. No longer was DD quiet and shy and holding back. She was talking in complex sentences and asking her questions. I guess it was enough for the teacher's mouth to drop. So I definitely don't regret my decision. Immediately upon moving her to the new school DD returned to the DD we knew ... because while at the other school her attitude at home had changed.
But if I were in your shoes I would definitely inform the teacher.
