A search in Google returns lots of studies and thinkings about teaching in undergraduate schools. Could anybody come up with any research/references about teaching in graduate schools (graduate courses taught by professors)? (When I search "teaching in graduate schools" in Google, what returns is mostly about teaching in undergraduate school by graduate students, which is not the topic I'm talking about.
A related book I have found so far is The Graduate School Mess: What Caused It and How We Can Fix It. But it is not directly about graduate education in mathematics.)