Lieutenant Chang, a tac officer in 2364
In Starfleet, TAC officers prepared and assessed potential cadets for entry into Starfleet Academy.
In 2364, Lieutenant Chang was serving as an Academy TAC officer at the Federation starbase on planet Relva VII. While there, he oversaw Wesley Crusher as he took the Starfleet Academy entrance exam. (TNG: "Coming of Age")
"TAC" stands for "Training, Advising and Counseling", and TAC officers oversee the instruction, development and evaluation of cadets or candidates undergoing military training. TAC officers were used at a number of military training facilities, including the United States Military Academy (USMA), The United States Air Force Auxiliary Cadet Program (Civil Air Patrol), and the Warrant Officer Candidate School (WOCS).