Drawing is an interesting, experimental activity that heavily dwells on observational skills aside from the cognitive and affective domains of the students an instructor tries to dwell on to improve their drawing skills.
Using practical oriented teaching approaches is always the best for teaching drawing. Assigning creativity driven project works and careful utilization of exploratory methods of teaching works well in developing the drawing skills of learners.
Demonstrative teaching methods also yields much learning outcomes where the instructor personally demonstrates how a particular drawing task is carried out before asking students to mimic (This is very important in the foundational teaching of drawing for students to grasp the basic concepts).
I have attached these two excellent resources that art teachers could use to bolster their teaching approaches in drawing. Kind regards