International students often comment that U.S. students are competitive but don't seem to study very hard and that in spite of the informality of the classroom, the professors are very demanding. Some of these apparent contradictions can be explained by the values that underpin them. Creativity, tolerance, and flexibility are, in general, valued above tradition and respect for authority in the United States. Teaching styles and classroom attitudes vary widely and are influenced by many different factors. Even where tradition does dictate professorial or student behavior, the patterns may not be evident to someone coming from a different tradition.
Professors are the core of the teaching staff at most institutions in the United States.
Full professors generally teach lecture courses, seminars, and courses for graduate students and upperclass undergraduates. A professor's informal style of dress or speech must not be taken to mean that he or she has a relaxed attitude toward assignments, class attendance, or the quality of your work. Teaching assistants are most often graduate students pursuing a masters or doctoral degree. You should feel free to approach them with your questions indeed, you will probably be on a first-name basis from the beginning of the course and you should not hesitate to ask their advice about course work, grades, or other matters. Since research universities began operating in the United States, graduate students have assisted professors by teaching undergraduate students.