Sorry to hear that!
We visited a Montessori that goes up through 8th grade and the higher levels didn't seem to be doing "baby" things at all. It really was more like a college atmosphere in the upper elementary. Kids could decide to work in the library if they chose. Each child met with the teacher at the beginning of the week and negotiated a "plan of action" or things they would accomplish academically for the week. Students were then allowed to accomplish those things at their own rate, but they did have to follow-up at the end of the week to ensure they did accomplish what they set out to do. The freedom was very nice to see and the kids we saw working in class were doing what seemed to be pretty advanced math.
Hopefully you will find another school to at least observe. I would love for Mite to find an atmosphere that allowed him to be his wonderful self!!!