Teaching assistants are enrolled into the course with a combination of development responsibilities. This includes the ability to develop test questions, verify grades, manage users, and many others. The role of a Teaching Assistant is assigned by the course instructor.
www.blackboard.niu.edu/blackboard/glossary.htm

A Teaching Assistant is a registered graduate student in full-time residence, chosen for excellent scholarship and for promise as a teacher, and serving an apprenticeship under the active tutelage and supervision of a regular faculty member.
gradstudies.ucdavis.edu/old/support/tadefinitions.htm