I agree that being "able" to skip and deciding to do it are 2 different things & what is important is how you and your son feel about it. I would really suggest trying the skip to 4th grade before going further (it doesn't mean you can't switch him a month later). I think skipping presents a number of challenges, including social adjustment, disciplinary, learning how to write X type of report, etc. My 4th grader is a YS and skipped once, but he could skip more--he does so many cool things at school and is currently enjoying Harry Potter books, ALEKS, accelerated math, literature studies, science technology lab, researching topics, field trips, etc. It is not wasted time. He has a lot of friends of different abilities. It depends what you see for him and what he wants for himself (may be difficult to decide since he's young).
My 2 oldest sons they feel they were at a disadvantage to have been smaller than their friends (they went through puberty about 2 yrs after because of age disparity). They both say they would not want to skip again, but one says he'd like to try to finish high school in 3 yrs, then take a year off before college doing something interesting. Oldest son actually wants to finish in 4 yrs and then take a year off to go to college older. He feels insecure about his younger age--though he's "able" to have skipped additional grades.
