A few good books to read:
IOWA acceleration scale manual
5 levels of giftedness
Genius Denied
and look at a few websites:
www.nationdeceived.org/http://davincilearning.wordpress.com/2010/08/03/oh-no-my-kid-might-be-gifted-where-do-i-start/If he is tested gifted, the next question is LOG (level of giftedness)
If he is optimally gifted, which is the majority of gifted kids, then staying with agemates and doing the gifted program is likely to be a good fit.
If he is a higher level of gifted, then you have to look very closely at all the options, including going to a higher grade - unless the ideal happens, your district has a program for Highly Gifted and Profoundly Gifted kids of the same age.
Basically, you want to keep you child spending lots of time with kids who are academic peers in hopes that your child will develop good work ethic and have fun with kids who get his jokes - that may mean a gradeskip, or it may not, depends on the local resources.
Lots of the folks who post here have kids who are beyond optimally gifted, but that's because many schools have great programs for their optimally gifted kids and it would never occur to the parents that they have to seek out more info - logical, no? So don't generalize from what you read here if it isn't needed.
A visit to the various potential classrooms will go a long way to figuring out what might work.
We welcome you to keep posting no matter what your kid's IQ score says! Yippee!
Grinity
