The American Boychoir School (ABS), in Princeton, New Jersey, is one of the premiere boys' choirs in the country. I would like to say it is the best, and I honestly believe it to be so, but I have heard several other good choirs out there, so I know ABS doesn't have a monopoly on talent.
ABS is a boarding school for boys from fifth to eighth grade, though I arrived in fourth grade, and at that time third graders could join. Since then, the choir has grown and now prospers.
The Boychoir is not a music school: most of the students will not go on to musical careers (I myself am studying Physics). It is a normal school academically, though the boys will often have to do weeks of tour assignments on a bus rather than in a classroom. It is also the only middle school I can think of with mandatory nap time. This may seem silly at first, but the schedule is so demanding that except for the few days our rest period was completely unnecessary and I itched to be outside, I wished it were several times as long.
The Boychoir, at least in my days there, had a wonderful faculty.
We also played some wonderful games, which I recommend for anyone trying to figure out what one can do to keep sixty-five or so boys in between ten and fourteen years old active but not beating each other up too badly.