MDmom - all IQ tests are pretty unreliable at that age, some kids do test higher than they eventually will due to very rich home environments, some kids will test lower (even WAY lower) because they ate the wrong thing for breakfast or don't like the tester, or any other thing that might put a 3yr old off their game... BUT when you are talking about it in the context of what a school requires for entry to their program - it's no more or less reliable for your child than any of those other children. Unless of course yours is the kid that refuses to do the test properly...
My DD did the WPPSI3 at 4.75 yrs and refused to do one subtest properly. It pulled her score down enough that we retested again later, but she still scored high enough that she would get into most gifted programs (99th percentile even with the test she was difficult about).
In terms of schools - my personal belief is you really have to look at the particular schools near you and think about your particular kid and see what feels right. Montessori can be done so badly or so well, as can gifted schools. There are kids here who have thrived and who have crashed and burned in schools that sound a like. There is at least one child whose had an awesome year at a gifted school and then been badly damaged by a different teacher at the same school the next year... It's so individual and it's never straightforward.
