I went to boarding school, and it was a really rewarding experience for me, but it is not for everyone. That being said, each school is different and there are many options- even in the US. Most prep schools here are on the east coast, which is unfortunate if you live far away and like being relatively close to home, but there are a handful of others scattered around the country.
I actually went to two different boarding schools during my high school years- one for three of the years and another for a year in the middle as a sort of exchange program. Both were in the US. The first was one of your classic, preppy, prestigious boarding schools. 600 students, as well as an endowment (and low acceptance rate) to rival many colleges. I loved it. The academics and the athletics both were challenging and rewarding, and I made many great friends there.
I also loved the school I attended for just one year. It was about as different a school as could be. There were only 80 students, we called our teachers by their first names, and there were no grades. (This last part was a bit tough for me, having been a competitive perfectionist all my life. Also hard was the fact that the only had one sport: soccer, and it only ran in the fall. I had always been a three season, varsity athlete, so I was forced to try some different things.)
Both schools had fantastic communities, and they were equally wonderful even though they were completely different. I don’t think I would send my children away any earlier than high school. For me, at least, freshman year was the right time to go to boarding school. A big plus with these kinds of places is the exposure that you get- to people from other cultures, to opportunities you would never see elsewhere, to people with similar goals. And I realize that this is NOT the point of all this, but the reputation of my school and the grades I got there made it so that I really had my pick of colleges when that time came around. My schools prepared me very well.
Sorry, that was a bit rant-y, but I know some people from outside the boarding school community that I think would have benefitted from this kind of experience, so I just want to advertise it, I guess. So that people consider it.