Half of the teachers I've had so far would do anything to help the advancement of students. If a student was having issues learning particular subject material, they were more than willing to restate it or work with the student(s). The other half seem to be there only during class time and never during their office hours, and are unwilling to help the student. One instructor in particular almost acts as if it's a bad thing for a student to ask a question during class, and often ignores hands. Later, students may email him those questions and get to response in return.