That is a good point. It's worth looking at the full range of options all the way out to college, as quite a few states offer various levels of free or subsidized dual enrollment community college or 4y university courses.

A few organizations are active in promoting DE/EC, such as:

Middle College National Consortium (http://mcnc.us/)
National Alliance of Concurrent Enrollment Partnerships (http://www.nacep.org/)

And many of the states that have a well-structured DE program run and accredit their own programs, often with automatic acceptance of DE credits 1:1 at state universities. You can check with the state DOE and BHE (Board of Higher Ed) for that info. E.g.,
Washington (https://readysetgrad.wa.gov/dual-credit)
Michigan (https://www.michigan.gov/mde/0,4615,7-140-81351_40085---,00.html) (EC is linked from that page)
Massachusetts (https://www.mass.edu/strategic/earlycollege.asp) (DE is elsewhere on the same site)