Several high schools in Colorado partner with the University of Colorado where they can take CU courses at their high school. They are the regular collegiate classes and show up on your CU transcript. The program is called CU Succeed.If you're willing to move to Indianapolis, there is a high school there called Ben Davis University High School (part of Ben Davis High School) that allows students to graduate with an associate degree from Vincennes University. I'm sure there are many other schools that do that, but that's the only one I know.
Depending on the school (each school differs on how many classes they offer) many kids have started CU as a second semester sophomore or first semester junior after they graduate high school.
And each class is only $250, so you save a ton on those first 2 years of tuition.