Rod Jenkins outlines a very thorough approach in his section of Masters of the Bare Bow 3. For the first class, I would alternate between brief discussion sessions and brief shooting sessions. Maybe start with 10 minutes of introductions and history of archery, followed by 5 minutes on the first form element you want to discuss, then 10 minutes of practicing that form element at the blank bale. Then alternate between brief discussions of various form elements and brief blank bale practice sessions for the rest of the class. The class should be small enough that you can offer individual advice during the practice sessions.
If you have a follow up class, it should be at somewhat longer ranges and different elevations, so you can work on things like stance on uneven ground, canting, peeking, and maintaining the "T" of shoulders and arms that usually aren't problems with the blank bale.