Investigate Advanced Placement courses. AP classes are college-level courses taught in high schools. If you pass a test at the end of the course, you get both high school and college credit.
Check into dual or concurrent enrollment. High school instructors teach these college-level classes, but they differ from AP courses in that the teacher bases the grade on assignments throughout the course instead of a single final exam.
Find a community or junior college. Some allow students to take courses for a limited number of credits before graduating from high school.
Contact an adviser at a community or junior college. Many offer programs to help those who want to get college credit but never finished high school, such as non-traditional student programs that allow dual credit.
Consider a GED. Most colleges consider a GED equivalent to a high school diploma. You may be able to take a certain number of college courses before you pass all the GED tests.
Explore lots of colleges. Some institutions no longer require a high school diploma, such as Rockland Community College in New York.