Advanced Tactical Training is a special course for Starfleet officers. Officers must be recommended for this training. It is so difficult and challenging, in fact, that half of the class washed out each year.
Ro Laren attended Advanced Tactical Training per the recommendation of Captain Jean-Luc Picard. After her training, Admiral Alynna Nechayev felt that Ro's training qualified her for an infiltration mission of the Maquis. Ro was hesitant and even mentioned that one of her instructors in Tactical Training (a lieutenant commander) was sympathetic to the Maquis.