Well I would have to respectfully disagree with this, it really depends on the kind of environment they are put in. Like I stated, we still had a "high school" it was just located on the college campus. We took college courses, but still had a "school" to go back to. I didn't really hang out with the college students too much, but had tons of friends from my school who were my age and interested in the same things as me. I blew through our traditional high school's course work, and wanted more of a challenge. I don't ever regret the decision my parents and I made. They weren't trying to push me to say they had a child that graduated college at a young age. They let me make the decision.
And I will tell you something else, almost all of the kids I went to school with are very successful, and well-rounded individuals. Most have gone on to pursue Master's. Others who were able to participate in the wonderful arts program at our college have gone on to dance on Broadway and with traveling Ballet companies. One of my fellow classmates is even in MIT in the Astronautical program training to become an Astronaut.
There was never a problem with drugs or drinking in our school. No cliques (granted we didn't really have enough students to have cliques). Everyone was friends with everyone else. We all were there for a common goal.
While I do agree with you that most 16 year old's are not ready for a college environment, please don't stereotype all of us. It was very difficult at times and required a lot of discipline on my part. It prepared me for a four year University in a big way. I knew the structure of college coursework and still had a blast in college!!
This doesn't work for all people. Like a pp said, if your child is very into the high school experience it's probably not he best option. At our traditional high school, I was one of those kids who didn't have a whole lot of friends. Ate lunch in the library while I studied. Even had a few girls who were very mean to me, just because I did well on my school work. When I went into the high school/college program I flourished. I made many friends who are still my best friends to this day! I ran for our student government, participated in school activities, and even helped organize some of those said activities. It doesn't work for everyone but I am so blessed to have been a part of such a wonderful experience!!