A graduate teaching assistant assists in running classes at a university. This may include helping a professor teach an especially large class, grading papers, running classroom related errands, and performing other menial tasks at the suggestion of their overseeing professor. At some schools, experienced graduate teaching assistants are given their own class to teach, and only meet with their assigned professor occasionally to discuss the matter. The classes that they teach are usually introductory courses in their field of study. For example, a graduate student studying English Literature will generally instruct or assist in instructing a Freshman Composition class, or a similar class within the field.

Graduate teaching assistants also sometimes help professors complete research. Assistants in the sciences may work preparing, setting up, and cleaning labs and scientific instruments. They may also work in university-sponsored tutoring centers, helping undergraduate students succeed. For example, a graduate student in Physics may work at a university tutoring center assisting introductory physics students in understanding ideas in their courses that they find to be complex. Graduate teaching assistants perform many jobs that professors are not interested in or consider to be menial or tedious.