The trouble is that my son is very shy and takes a long time to transition to new situations. He's never been to preschool and already hates the idea of going to school. He even cries at the idea. (I'm a teacher, so obviously I've talked plenty about school and how fun it is. We've even visited several!) I want to do the right thing for him. Would it be better to keep him home a few more years and let him become more social at his own pace? Or would I be making things worse by keeping him out of the "system" and making him transition at a time when all the other kids are used to it? (We've decided we don't want to homeschool past 8th grade if we did it.)
There are three issues here to consider:
1) Your son's social personality. From my experience, shyness is not "cured" by going to school. Nor is shyness "created" by homeschooling. Kids are either slow to warm up to new people, or they are not. You said that your son is fine once he gets to know people. This is a healthy and perhaps even preferable way to make friends. People who are "sociable" aren't necessarily better at making friends. And, he's only 6. He has plenty of time to grow into his personality and learn which social situations he's comfortable with, and which ones he's not.
My daughter is almost 6, and she is "shy" in some cases, and not in others. She (and I) have learned when she's shy. Classroom situations where she is studying something she doesn't want to do is one of those places that she's "shy". Actually, she's not being shy, that's just her way of withdrawing when being asked to do something that isn't a good fit for her. You get her in a place where she's enjoying herself, and she's very outgoing. She also makes friends quickly in those situations as well.
For some, school is the "right" place for their social personalities. For others it isn't. School doesn't cure people's personalities. It either fosters it, or it doesn't. Same with homeschooling, although I would argue that homeschooling is far more flexible and adaptable to a wider range of social preferences.
Once you and your son get to know what he likes, and once you get involved with some groups and activities, his shyness will probably lessen. And as he gets older, if you focus on helping him feel confident in who he is, and confident in his abilities, he may always be slow to warm up to people, but it won't matter because he'll be confident and quiet. My hubby's like that, and people like him a lot for it. Being quiet and introspective is not a bad thing.
2) He's working at a nearly 2nd grade level. What this means is that school won't teach him anything right now. Being so ahead of his peers might actually make him more uncomfortable and withdrawn. So, if he's not going to learn anything, and he's going to be uncomfortable and feel pressure to be something that he's not because it's not OK to by shy in school (you can tell it's not OK to be shy in school by all the responses about how you should send him to school so he won't be shy), then what's the point of sending him to school?
3) You're moving. If you guys have a good family rhythm going on, and he's adamantly resisting the idea of school, why send him? Moving is stressful enough. Let him be where he's the most comfortable, and where it will be the least amount of stress for your family. After you move to your new place, and settle in, maybe he'll change his mind and want to go to school to meet the kids in the neighborhood. Or maybe not. Either way, you won't know until you get there.
Hope this is helpful. Good luck!