Many gifted young people are ready for college-level work before they officially graduate from high school. When they enroll in college courses at the same time they attend high school classes, this is called "dual enrollment" and, according to this recent article in the Omaha World-Herald, the practice is catching on. At least four districts in the Omaha area, the paper notes, are planning dual enrollment programs.
Of course, if this conjures up images of kids actually going to college campuses, that appears not to be the case in Omaha. Local colleges contract with high school teachers, approve a syllabus, and the teachers teach at the high school itself. So on some level, one could just call this more rigorous high school classes... which (unlike, for instance, AP classes) students have to pay for by the credit hour.
On the other hand, they don't have to pay much, and they do get college credit. Since college isn't cheap these days, this means students who enroll in local colleges can save some serious money on tuition (a point the particular reporter who wrote this piece seems mildly obsessed with). Even those who don't will probably benefit from more challenging coursework. So, on the whole, if this is catching on, I think it's a positive development.