Ezri Tigan graduated from the Academy and was an Ensign as she served as an Assistant Counsellor, still undergoing what seemed to be an additional year of training upon completion of her studies.Makes you wonder...was Troi ever an Ensign or did she graduate with the rank of, say, Lieutenant due to her position as a counselor?
Deanna Troi entered the Academy in 2355 and graduated in 2359, but sometime between 2357 to 2361 she and Riker were dating when he was assigned to Betazed. She could've done a couple years at the Academy campus on Earth, then transferred to one on her home world (perhaps one that specialised in psychology, diplomacy and social sciences) when she went into her third year and stayed there until she graduated. Between 2359-2360 she may have taken an assignment at the Starfleet complex on Betazed as she completed her time as an Assistant Counsellor and was promoted to Lieutenant (jg). She then had four years to go up another rung on the promotions ladder and likely got her Lieutenant Commander pips just before being assigned to the E-D in 2364. For such a meteoric rise, she must've been doing something right, or at least impressing the right people, I mean it took Riker seven years to go from Ensign to Commander, and she made it to Lieutenant Commander in just five

Since she can't work 24/7 then I'd assume there were at least two other counsellors onboard, to have one per shift.Which also brings up the old question about how the counseling/mental healthcare staff on Star Ships was organized. There simply had to be more counselors than just Deanna for a ship of 1000+ people. She probably was the "Chief Counselor" or something...it also brings up the question whether the other counselors also wore civilian clothing.