I offer a 30 minute Chant Class before our regular rehearsal (FSSP parish/ Full Gregorian propers) and teach the basics of reading and sight singing plain chant. My inspiration was actually a swing dance club that I went to once in high school, where the first 30-45 minutes was a beginning/intermediate swing dance lesson followed by a few hours of dancing. The idea being that those who were still learning could come earlier and those who knew how could come at the regular time. That way those members who are less experienced have a chance to get my full attention without having to beg the patience of those who were more experienced.
Mostly it is the younger choir members who attend, but it does seem to be bearing some fruit (This is the second year). Mostly I teach the sol-feige method, mostly useful for chant, but I would expect something similar would be possible for Western notation as well.
I don’t give homework, really, as I hope that the rehearsal itself will provide an immediate opportunity to exercise what we covered in class.