On the default being male -
Menstruation is a biological function of the default healthy female. On average that means a healthy female is affected in one out of every four lessons.
If females were the default, scheduling principles would have developed taking this into account from the outset, ie when regular swimming lessons were first offered to the public.
Please note, the default is not just the average male, but the average healthy male.
So not just the average male.
And actually we are talking about females who menstruate, so not post menopausal women, pregnant women, or pre pubescent girls.
And come to think of it, we are only really talking about that very small subsection of girls and women who for some reason do not wish to use a tampon. Despite the claims here, that subsection is actually very small.
Yes, it would be nice if pools offered flexible scheduling. However, a course of swimming lessons is often designed as a series involving progression from one skill to the next, combining previously mastered skills, at least in the initial lessons.
I suppose the various strokes could be mastered in any order.
As a swimmer myself who never had actual lessons but was taught the basics by my dad, and who managed to pick up different strokes from watching others and practicing, I am not sure how serious the issue of missing some of the formal lessons is.
Mostly what you develop in the course of swimming lessons is confidence that you can in fact float.
What you develop outside of swimming lessons if you have access to a pool is strength and endurance, and you can also fine tune your strokes.
You can develop the necessary arm and shoulder muscles for swimming lengths in your sitting room. Most competitive swimmers lift weights and run on top of spending time in the water.
What I am saying is, missing a few lessons is not going to make or break your chances of learning to swim or even to swim fast or well.