An individual assisting a teacher with instructional responsibilities is a teaching assistant. Usually a graduate student assists in undergraduate course in his/her field. Teaching assistance is a non-profit service. Various teaching assistants are graduate teaching assistants, undergraduate teaching assistants, secondary school teaching assistants and elementary school teaching assistants.
In the U.S., teaching assistants receive course credits in return for their assistance. Usually a graduate teaching assistant in a university or college is awarded a fellowship that provides him or her with financial aid in exchange for teaching duties.