Well, it does when it isn't working! I dance with amateurs, too. If I'm not clear about a lead, or if something doesn't feel right and I don't know why, I always phrase my question/comment in a neutral way, so it might fall into your "only comment on what the other person is doing if asked" criteria.
But when we know we're working on making our promenade runs have the proper spacing and actions for 20 minutes (real-life example) we spend 5 minutes reviewing all the info from our lesson, then zip the lips for the next 15 while we repeat ad nauseum. Bulk of our practice time is in this mode, especially since most of our choreo stays unchanged for a year at minimum.