I know D20 has some International Bacculaureat (IB) high schools where you can get 1st year college credit.
Check
www.ibo.org
I checked: Rampart H.S. and William J. Palmer H.S. in Colorado Springs.
IB schools have to meet additional stringent requirements above state and federal requirements. The IB schools are also worldwide allowing easy transfer between schools (same level of education). My daughter started out in an IB primary school where she had French 3x a week in Kindergarden. Now she is in the French immersion program in 1st grade in Colorado Springs (they teach math and science in French in addition to French language classes).