Why does Katherine care if Betty misses class? Katherine's not paying for the classes and Betty's an adult. Katherine's salary is set, right? I went to college and never understood why a few (not all) professors tried to influence students' attendance by docking their grade for not showing up. Some classes I can see it because being there and actually participating is integral to passing.
shareI don't think it was necessarily the fact that Betty missed classes as opposed to the reason why she missed them, coupled with the fact that the faculty was supposed to "look the other way" when a student set up their home post-marriage. Attendance was important to Katherine because being present was how the students learned (remember she stopped utilizing the syllabus after she realized the entire class memorized the materials before the first day of class). She wanted the girls to look at things differently and realize their full potential (i.e., have careers of their own) as opposed to going to college to end up as housewives, which is where most of them would end as up despite her efforts. Allowing them to miss multiple classes, in Katherine's mind, was implying, "Being married is the only thing, and your education comes second." And that's not what she believed.
shareAlso, she missed a paper and her midterm. It wasn't so much that she missed a few classes - she missed major assignments, too. A paper and a midterm together could easily combine for 30% of the final grade, or more. And not only had Betty not done either, she very obviously didn't care. I'm actually surprised Katherine was as restrained as she was in that scene. It wasn't the first time she had called Betty out for her attitude.
shareAs a teacher of fifth grade, a far difference from college, it's frustrating as your student isn't receiving the full brunt of their education. If an assignment is due, needs to be explained the teacher has an obligation to provide that to the student.
It's hard to appreciate and make the extra effort for a student who uses and abuses the system. Betty expected more consideration as she had the gold prize: a ring and a husband before she graduated.