I didn't do weekly swimming lessons with my son when he was 4 (standard starting age where we lived), because he really didn't want to, and I had a small baby and couldn't face committing to something pointless every week for years - I'd seen him in a school group swimming lesson, and he just larked around with his friends, did sword fighting with the woggles, virtually ignored all the instructions, then 'swam' across the pool with his feet on the floor.
So we ignored swimming for 2 years. Then, age 6, I booked private lessons with a tutor. Straight in the big pool so no feet cheating, no playing around, solid instruction for 30 mins rather than daydreaming at the side waiting his turn. He could swim the length of the pool on his back within 6 lessons, and on his front within 10. Around the age, funnily enough, that the weekly swimmers managed it too.
In just 10 lessons, he'd learnt 3 strokes (not the proper crawl with breathing underarm, had to doggy paddle for breaths), could swim underwater through a hoop, pick up underwater objects, float on his back and front like a starfish - all sorts of things.
I just did the same thing with my daughter this summer, aged 6.5, although she was even quicker - swimming about 10 metres by the end of the 2nd lesson.
So although I firmly agree that swimming is an essential life skill that's best to acquire as a child, it doesn't mean months or years of turning up at the municipal pool at 4.45pm on a Tuesday (aren't the time slots always desperately inconvenient for feeding younger siblings?). Simply leave it a year or so until they have sufficient muscle development to bring their head out of the water and hold it their for breathing (usually age 5 minimum; before this they can swim well underwater, then put their feet down to breathe), enough coordination to quickly grasp the strokes, and enough brain development to grasp 'As soon as you've got your length/Level 3/whatever certificate, you can stop the lessons' (if they're not that keen).
Then book private lessons at a time convenient for you - a course of 10 will be ample.
Job done.