yup any of the "freinds schools" are good, as they are based on quaker philosophies, which in my opinion can be a very positive influence on a teen's life.
the problem with boarding schools is that although they may be more "stuctured", problems still exist. for example - most boarding schools are full of rich kids, as they are highly expensive. so expect alot of spoiled kids driving BMW's who do lots of coke on the weekends. Some schools take the structured thing too far, and are borderline abusive and could almost be considered lockdowns (e.g religious single-sex schools).
A good middle ground would be to find a school that is primarily a day school, but has a number of boarders. for example, Maine Central Institute. They are a great school - one of the top in the country. but it's also a public school for the kids in the county, and a private day school for kids out of county but within driving distance. so you have a whole variety of people - white kids, black kids, townies, hicks, suburbanites, city kids, and a variety of nationalities of boarders: Japanese, Chinese, Caribbean islanders, europeans, russians, canadians etc.. you also get quite a bit of freedom while still being structured.
there are still a few problems with the school. Prescription medication abuse is rampant (vicodin, oxycontin, xanax) as it is in the rest of maine, but mainly among the locals. There are outstanding kids there, but there are also many no so great kids there - junkies, teen mothers, a few local impoverished quasi-homeless kids. they all go to the same school. If your big on weed - theres plenty to be had in the fall. the problem is that it's generally pretty crappy stuff and the place runs kinda dry between november and may, hence the pill popping. The town is pretty poor and theres nothing to do. also, between november and march the days get really short and the temprature hovers around -10F.
the school will give you structure and supervision, and separate you from your current environment. BUT, if you think you will fall into popping pills, get depressed in the winter, and think your more likely to hang with the junkies and homeless than the internationals, then the school is not for you.
otherwise, MCI is a great school.
there are some other schools that are more on the "theraputic" side, but are still very liberal and dont restrict you that much, for example the king george school in vermont. Watch out for schools that claim to be "traditional schools" with theraputic elements though, such as hyde or hidden lake academy.