I had a teacher like that in high school. He taught AP/Honors government and had some of the highest pass rates for any teacher in the school. He stayed after school for a fixed time - 30 or 45 minutes - no longer - and most of that was spent with students. It took him FOREVER to grade tests and assignments. But, he was one of the best teachers I had in those 4 years and I, along with most of my peers, aced both exams that year (he did AP US gov in one semester and AP comparative gov in the other).