Amber,

Couple of things. First the writing comment. Have you tried to mask writing in a fun activity? One that crosses my mind is to make a soft paste in a cake pan and have him write his letters with his finger. I'm sure there are many others and the OT should have lots of ideas.

Second, given your description I think I would try the gifted school. Have you contacted them? You could ask them how they handle lack of interest or boredom. I, too, would be hesitant to jump to the conclusion of ADD. When the psychologist did his/her testing did they hint at ADD? Time will tell if this really is the case but for now I would chaulk it up to not a good fit. Montessori schools are not all the same and depending on the teacher and the school policy it could be too rigid for what your little guy needs.