For 11 years, I was one of the instructors of the Basic Indexing course for the Graduate School (formerly part of the USDA's correspondence programs) . This course is no longer offered by the Graduate School.
In the new millennium, this course provided a solid foundation in practical indexing skills. Many publishers can attest to the high quality work produced by indexers who took this course.
The version of the course I taught was created by Nancy Mulvany and later revised by the instructors (all successful, professional indexers) working in tandem with instructional design experts. (That said, at the time of the revision, a couple of the instructors said they were too busy to help with the revision. Sadly, they later claimed publicly that they were excluded from the revision process.) The course greatly benefited from having instructional design experts work with us because they had a greater understanding of adult learning theories and practices.