Mechanistically, understanding a concept is bridging two or more existing neuronal circuits through new synapses. There are more than one way to activate the existing circuits. Classroom participation, if possible, is another. Homework is yet another. I advocate a better use of visual input.
All primates are highly visual creatures.
It is a great waste to ask students to watch the lecturer for 50 minutes a stretch while she gives them verbal messages. There are instances where no number of words can convey a concept as easily and as deeply as an image. I can think of two reasons. The image evokes and excites existing circuits not easily reachable by words. This is not to simply advocate a better use of visual aid.