correspondence course 
noun
A course of study in which student and tutors communicate by post.We already tried a high school correspondence course through the Distance Learning Program, with which she had no trouble....
- If the sickness extends for a long time, you may want to consider enrolling your children with a home-school correspondence course.
- He enrolled in a correspondence course to develop his art, but long, hard hours meant that he couldn't keep up with the work.