Consider carefully and closely what those social aspects are. Check that your perception matches reality. For example, in the classroom, 90+% of the time students are supposed to be quiet, or to interact with the teacher (usually answering a question—in front of, but not with, the other students). Most of the social part of school is interacting with friends at recess and lunch, and sports and non-class activities.
Furthermore, the parts of school that are social are not necessarily good: for some people, they consist of being rejected or even bullied, and making them suffer that for years may lead to socially avoidant habits, anxiety, or other long-term issues.
As eloff suggests, sports and other activities are a good way to get good socialization. Since the activity is voluntary, all the kids can be expected to share at least one interest with your kid. Also, if your kid meets some people he likes, then what are called "play dates" (at young ages) or "hanging out" (at older ages) can lead to deep, long-term friendships.
I left high school at the end of tenth grade, but continued going to the math club and attending an after-school math contest class, and hanging around in the math department's common room with others who had a free period before that class. The school was happy to allow it because I was good at the contests, and it made the school look better to let me participate. I got about as much socialization from that as I did when actually attending school, and I was happy with that.