Well, I was teaching a Materials Engineering 101 class of 134 students. This was a required class for some of the other engineering tracks. It's the kind of class assigned to graduate TAs. Needless to say, even though I was teaching in person, there were plenty of students zoning out in the back rows. After that I turned down all undergraduate teaching tasks, except for seniors on special topics. At least those 10-15 students were motivated.