I have been teaching on this topic for many years and I have largely
had the same experience. However, increasingly I am finding a small
group of students who are extremely knowledgeable. This make teaching
very interesting as you have (on the one hand) many students who have
no background, and (on the other hand) a few advanced students. I have
begun to address this issue by giving them self learning tasks where
they select (in consultation with me) a topic that the would like to
learn about. They then conduct an annotated bib on the topic. THis way
whatever the knledge-level, the student can find something that will
gain their interest and motivate them to learn.