Rather surprised no one has mentioned the use of a model, such a good teaching aid. No not the "Victoria's Secret" kind of model either, but a model aircraft! PPT is ok, but yes you should be able to whiteboard talk/draw also. Using a model I think, is good to point out relative airflow/AOA measured on wing chord line, all easily shown with pointer and model, explain root to tip stall, the model is great to show how the root stall causes a useful warning of a light buffet over the elevators and can be used to 3 D illustrate increasing AOA, to critical angle. So as I feel like rambling on......
Start with defining a S+L power off basic stall, then going onto the very important fact that critical angle can be achieved at much higher speeds, and the aircraft safely flown at speeds below basic stall (below crit AOA). So to me, in the air, basic stall and recovery demo, followed by the vital demo of when there's heavy buffet - you're stalled, regardless of speed or flight attitude. I was shown this and shown a sortie flight profile by my ex RAF mates whilst instructing with RAFOman on Masirah Island. I thought it was a very good method, especially the demonstration of heavy buffet (a G stall at above basic stall) you're stalled, no buffet (a gentle bunt from a steep climb, to show flight at below basic stall) you're not. Unload - till buffet goes away, not stalled.