The ATS is the most recent PSIA system to integrate teaching, service and skiing models in the US. A full reference is from PSIA Manual.
The basic teaching progression starts a student with balancing on a moving ski on a flat area and progresses to 2 skiis, making a wedge turn in each direction, and stopping by turning uphill by stepping out of the position. Once the student can turn both ways and stop on command on a gentle slope, edging of the skiis by side stepping up and downhill and climbing with a herringbone maneuver is introduced and the skill is developed to let the student climb and slide on a gentle slope. At this point the student is shown how to ride and unload from a beginners lift, the next stage is to ski a great deal and to practice the 3 skills they have been shown and to learn about pressuring the ski edge.
I teach this in about 1.5 hours in a large resort. 5 days a week, the next lesson will entail more skiing, and some new turns to help the student to become a good skier.