The tricky part was looking for a swim school which offered programs for both Z and X at the same timing.
Like how Mr H put it:
1) 3.5 yo child (able to swim, need to refine strokes)
2) 7 yo child competitive (achieved Gold Swimsafer cert)
X definitely needed a Learn-to-swim class and Z needed competitive classes because he wanted to work on stamina, endurance and speed.
We always preferred the idea of using swim schools because peer pressure could get the kids more motivated. Schools also tended to have a structured curriculum and clear direction on where the kids would be progressing to.
We considered the below schools due to proximity or familiarity.
3. Ace Swim club
All had their pros and cons, and Z was still moving through trials while X had to maneuver through assessment to see how many levels he could be exempted from.
At the moment, he could only skip one level. For the last few months before he turned 4, we would try to correct his kicking and breathing.
Otherwise, X seemed pretty excited about the concept of attending swim lessons. We could only hope that he would not be a prima donna about it.