It depends. For example, I just had a class of nieces and nephews, two boys, two girls, 12-15. In our family swimming well and comfort in the water come before walking... these kids had the mid-water concept down before ever getting in for pool one, and the skill to do it within about the first hour on scuba. Indeed, skills-wise they were done by the end of pool three and we spent two sessions just fine tuning, practicing and playing around. By the time we went for checkout dives at Vortex they were able to accomplish everything without ever touching the bottom, and were amazed and distressed at the rototillers around them mucking up the place.
On the other hand I've had classes where I had to watch like a hawk during the swim test for fear someone would drown, and was wishing I had some dynamite handy to blast 'em off the bottom and into mid-water during skills. While those folks couldn't reach mid-water mastery in the normal class time, they were at least low-level silters and not rototillers by the time we got to checkout dives, and more importantly, determined to get to be non-silters. So I think it's worth a try, even if you can't afford the extra time to make it "real" for everybody.
Rick