You've gotten a lot of great advice. Iowa Acceleration Scale Manual gives lots of explanations about LOG (level of giftedness) that helped me understand the various scores. But post anyway - nothing like a real person to talk to!
I would add that the key thing is to do a little sleuthing on your own to see what grade-level your child is able to function on - there are some nice recent threads about online assesments to print out. Then, once you understand your child as a learner, be sure to spend at least half a hour observing the teacher working in the classroom so you can get an insight into fit. It's easy for a school admin to say "Of course we differentiate for our advanced learners" but better to observe the teacher doing it, and ask for how the school would handle, A ____grader who is doing _____.
Unless you come from a family of team sport athletes, don't worry about size. Gradeskips aren't ideal, but very often for kids who are more than averagely gifted, that are the 'least-poor' option. The risks of 'enforced underachievement' seem much graver to me, based on my family's history.
Welcome and we're glad you are here!
Grinity