Teachers that don't know how to teach their subject. They may 'get' it, but can't translate their knowledge to their students.
Teachers that think that their students should come in with an understanding of their class, even if no pre-requisite is required.
Teachers in an environment that supposedly is encouraging of older students, who may have jobs and/or previous other commitments, who are inflexible where attendance is concerned regardless of the student's performance in class and on tests.