Some kids just do not do well in high school. Sometimes a private school can make the difference. I firmly believe that our kids did so much better in terms of education going to private schools. Some kids also do much better home schooled or in on-line schools or commuting to college. Those options take out the social interaction among their peers.
Traditional colleges do give weight to how a student interacts and performs among their peers and in their communities, which includes schools. If a kid is so strikingly brilliant that he accomplishes things that really knocks the socks off of the AOs, they’ll ignite the fact that he doesn’t do well in the sandbox and colors outside the lines. Otherwise, it counts against him. School and grades are not just a measure of academic performance but about how well a person can work with his environment and the people in it. Teachers, students, administrators all exist in college too, and when you join a college community, you need to know how to follow those rules and get those grades too. The selective universities in our country are trying to build a community, not just collect the best students.
I’m sure there are some, but i don’t know of any homeschooled or other such kids who did s lot of community college courses in high school get into the top schools. I was very active with a very academically driven home school group who did get have kids who got into major schools including Duke, Harvard and Pitt, but they did not do much dual enrollment with community colleges. Unless they are the only resource for a student in outlying areas, I get a sense that they are not given great weight in the college process. AP courses on line, or independently with very good AP exam results seem to be a favored way to go.
One does have to watch the rules about community college courses though When taken before graduating from high school, it’s not an issue.
Yes, the European schools, including St Andrews, Cambridge, Oxford and many lesser known universe may be good options for someone who doesn’t want to get involved in the typical student interactions of US residential colleges.
I knew one such young man some years ago who really had trouble in high school. He got accepted to a local college early. One can apply to college before finishing high school. OP’s son can apply this year instead of next. Schools like JHU, CMU, Stanford have been taking young kids for a long time now. A year early is no big deal. I have a number of friends, very close ones who were regarded child prodigies, went to college early. I also worked at a very well known gifted and talented program once upon the time. Not at all unusual to apply to college in the middle of high school. Heck, some were attending in middle school. So that’s a route that might be considered.