Montessori? My stepson went there... he's in 1st grade now, and he was tested for autism, but I really think he's only adhd, my husband went to his PT meeting but he's been catching up really fast lately.
It depends on the attitude of the school. The Montessori Method is PERFECT for ADHD kids because nothing keeps their attention more than working on things that they have chosen and the hands-on work is also very beneficial for ADHD kids. But - some schools have a very elitest attitude and aren't willing to work with the kids to make it successful for them.
If your school is open to the idea and are willing to be flexible then Montessori is a great option for your child. My son has combined type ADHD and is in first grade at a Montessori school near us and is doing wonderfully - UNMEDICATED! I give TONS of credit to the school and the Montessori Method for the fact that we haven't felt like it was necessary to medicate him. We are open to medication if it gets really bad, but so far the school has been really good about using subtle behavior modifications with him and the Montessori environment lends itself well to catering to an ADHD mindset. PM me if you have more questions :-)