The time-honored and dishonored method of lecturing relies on stimulating the receiving brains through audio input alone. There are other ways to reach them. 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.