Hi Kpmoon,
Welcome. I hope we can help answer some of your questions.
Quick question of my own is G4=fourth grade and G12=12th grade? That does sound confusing, especially if you don't think your child could read 12th grade textbooks by observing him at home.
1) There is no such thing as a standard definition of gifted. I try to see it as 'unusualness.' How unusual is it for kids at your son's school in G4 to be reading at G12 level. If there are 5 other kids doing that, then it's pretty likely that the teacher is creating classroom content that works for those kids. If, on the other hand, there are no kids higher than G6 except your son, then one wouldn't expect the teacher to really have enough time and energy to make a whole separate curriculum for one child. Although it has been known to happen, it hardly even happens more than one year in a row.
Kids who have an unusually advanced level of what they are ready to learn compared to the other smart kids in their classroom almost always continue to have an unusually advanced level of what they are ready to learn, until they get beaten down with boredom and disapproval and disappointment. Then they don't have less potential, but it sure becomes difficult to turn that potential into achievement.
Some kids like being unchallenged at school, and use school time to get their social needs met so they can go home and work on their personal learning projects. That can be workable for kids who are born focused and independent. I don't think that that is the majority of kids.
I would recommend reading lots of books on giftedness - just go to your local library and grab as many as you can find, and flip through them to snoop around and see what the variety of ideas are about giftedness.
One book specifically worth reading in your situation is
http://www.amazon.com/Re-Forming-Gi...ks&qid=1296156522&sr=8-1-catcorranother really good book is
http://www.accelerationinstitute.org/Nation_Deceived/Get_Report.aspxand you can download it for free - instantly!
Does your school have a 'gifted program' or a 'gifted coordinator?' - if so, I would call up and make an appointment with the gifted coordinator.
If not, I would call up and ask for a face to face appointment with your son's teacher, classroom or accelerated reading if that is a different person. I would ask what you have asked here (except the other options part - wink)
What does gifted mean to you?
You state most likely has a 'gifted association' - that you can join for about 40$. I would join and attend a meeting or event and try to talk to a live person on the phone if possible to find out what your state's definition of gifted is. You might get lucky and find someone who knows your school district well, or knows about other educational options that are available in your area.
Is homeschooling on your mind?
Love and More Love,
Grinity