@Cue7 It is definitely true that the vast majority of Penn classes are actually taught by actual Penn professors and NOT graduate students. Many classes at Penn have recitations on top of regular lecture times. These classes meet once a week and the purpose is for the TA to go over again the material that the professor went over in class and maybe also give out small quizzes and take questions. Grad students who are TAs also get valuable teaching experience from office hours, were students meet up with them individually or in small groups to ask questions and get help. Also they tend to teach some LPS classes and many summer courses. However not once in my experience at Penn have I had a class where the TA did the main teaching. It has always been a professor. On top of that, at least in my experience, professors also have office hours and are in fact very accessible to answer questions and help students deposited being very busy professionals. This has been an aspect that I have absolutely loved about Penn. It is a major research institution and churns out great volume and quality of research but the majority of professors who produce all this research really do care about undergrads too.