A research assistant is a member of a research group in a laboratory or on a project, whose principal duty is to contribute, under supervision, to a program of departmental or interdepartmental research.
The principal duties of a teaching assistant include assisting a member of the faculty in grading undergraduate quizzes and homework, instructing in the classroom and/or laboratory, preparing apparatus for demonstrations, posting web-based materials, and conducting tutorials.
For resources to support graduate students who teach, see Teaching at MIT.