Washington University in St. Louis has a 5-week program for students going into 11th & 12th grades.
I attended last year, and it was honestly one of the best experiences of my life.
You choose two classes and can earn college credit for them while learning alongside college students. The choices range from film to creative writing to psychology to math to foreign languages...there are so many choices. I strongly recommend it!
It's not exactly "prestigious" in that everyone has heard of it and it's nearly impossible to get into, but it does require you to be intelligent, and WashU is a very selective school.