Ditto on the plug for Montessori schools (although execution of the principles is all over the map, from what I have heard--so you do need to make sure the school really understands what Maria Montessori had in mind). My mathy DS was doing multi-digit addition and subtraction in kindergarten, long division before first grade (taught by a Montessori kid four years older than him over the summer at our kitchen table)...The school can totally support this while keeping him at the appropriate social level (in terms of peer age). They can also support that kind of acceleration (though that terminology is very un-Montessori!) in reading, writing, etc.
