It would have been in the early 1940s, I think, that my mother in law learned to swim. By then she was engaged to my future father in law, who lived on the coast so she thought she ought to learn. There was no pool where she lived, so she used the stool. Once she was married, she learned in a sea water pool before venturing into the sea. The teaching method there was apparently to tie a rope around your waist and someone would walk to the other end of the pool and reel you in while you tried out your strokes. Gradually, there was less reeling in and then the rope was taken away altogether.
For years she only swam in that pool or the sea. She said the first time she swam in a normal pool she almost drowned because she hadn't realised how much difference the salt water had made.
I hope TM will be relieved to know that I did not use either the stool or the rope method with my children!
As he says, there are a number of parallels with learning an instrument. The one that struck me most at the time was the variability in the quality of teaching between different teachers. When my children first started having lessons I use to sit and watch (there was a cafe area which was separated from the baby pool by a big glass window). Every time they moved up a level because they had reached a particular milestone I had to rejig our schedule to make sure that they could stay with the two teachers I thought were the best.