I happened to acquire the entire Folk School catalog the other day. The OD Campbell course is listed as the sole entry under the "Folklore" section and is a one-week course. There are many "folk crafts" courses - enamelwear, bee keeping, basketry, kaleidoscopes, felt hats, writing, etc.

Under Music, there's a lot on making and playing hammered & mountain dulcimer plus many on "folk" instrument skills - guitar, banjo, flute, autoharp, bagpipes.

And shape note singing.

Nothing else I can find on singing, song or ballad. Zip. Disillusioned am I. Maybe it's just that the likely attenders are already excellent at singing and simply don't need any instruction there.