High school summer programs at good Catholic colleges can be an excellent experience, especially for homeschooled teens, for several reasons including: motivation to attend college and valuable classroom and group-discussion experience.
Magdalen College gives young people between the ages of 14-18 a two-week experience of living on a Catholic college campus for study, prayer, sports, and recreation. Through the daily activities and close interaction with the counselors, the participants can learn and live the Catholic faith, acquire new skills in music, drama, and sports, and grow in wholesome friendships with others their age. The summer program provides an excellent opportunity for the participants to experience the spirit that animates Magdalen College.
Thomas Aquinas College offers a two-week high school summer program on their beautiful campus in Southern California. It provides an excellent opportunity to get a taste of their Catholic liberal arts program and the seminar style classes. Many summer program participants attend the college after graduation from high school.
Thomas More College of Liberal Arts For thirty-two years the Collegiate Summer Program for High-School Students has introduced participants to the same spirit of liberal arts education that animates the College. Each summer, the college offers two-week sessions that include course in literature, philosophy, the American political tradition, and apologetics. Readings include Faulkner, Flannery O'Connor, Plato, the Declaration of Independence, the Constitution, the Federalist Papers, Thomas Aquinas, C.S. Lewis and Guardini.
Note: This is a fairly old list from love2learn (clean-up will be going on for some time), but I did update the links. Please let me know ( in the comment box) of other programs that should be added to the list.