I realize I don't have nearly the experience teaching beginners that you have, but my experience for newbies is much less happy than what you describe. With the Retro Ripper rigs and (older) Start boards, newbies get up and going pretty quickly, but they (a) still fall off on the tacks, and get frustrated with having to try to lift the rig at whatever random angle it fell into the water at; and (b) still slide downwind (both because they can't "feel" the right angle to sail and because of (a)). Most of the people I teach take 2-3 sessions before they're confidently sailing out across the lake and back to their starting point.
I wonder if part of the problem is that I should get one of the newer boards with a kick-down centerboard(?). What's your favorite gear to teach a newbie adult to sail? My typical learner is 150-200 pounds, 30-40 years old, reasonably but not superbly fit. What conditions do you like best? We can usually find 5 knots easily (but it's flukey, so we don't usually bother), and 10 knots if we wait a few days. 15 knots usually leads to a bad experience, because the waves knock them off the board while they're figuring out how to use the sail to balance, so I go sail on my own on those days