Online Teaching Assistant Diplomas: A teaching assistant (TA) is an individual who assists a professor  or teacher  with instructional responsibilities. TAs include graduate teaching assistants (GTAs), who are graduate students; undergraduate teaching assistants (UTAs), who are undergraduate students; secondary school TAs, who are either high school students or adults; and elementary school TAs, who are adults (also known as paraprofessionals or teacher's aides). By definition, TAs assist with classes, but many graduate students serve as the sole instructor for one or more classes each semester as a teaching fellow or graduate student instructor.