The fundamentals of swimming are the same whatever the age of the swimmer - we all need the same set of skills in order to be safe and confident in water and to propel ourselves efficiently. Depending on the baby swim school, some skills may be taught or broken down in different ways, some things are given more emphasis than others, and the fundamentals could be taught in a different order, but all should be covered.
Baby swim schools group their swimmers in different ways too, depending on how they plan their lessons. For large national franchises, it makes sense for swimmers to progress up through a set sequences of lessons, levels or chapters, with one or two new skills introduced in order on set weeks. That ensures that all over the country one franchise works at the same pace as another - children could move to swim at a different pool with the same franchise, and they would slot straight in having completed the same skills. It makes teachers accountable too.
Working in such a way makes sense when you have hundreds of swimming teachers, but when you have just a few it's nice to have a little more flexibility. Every group of swimmers is completely different, and within the class each swimmer is individual too. It's nice to be able to work at the pace of the group, rather than a pace dictated by a lesson plan. Some weeks in my classes we cover three new skills with ease - some weeks I introduce a new hold and the children just aren't ready to learn it yet. Sometimes a group needs some more reinforcement of the skills we introduced the previous weeks, and some weeks a group of toddlers will have a special request for a song or activity we haven't done in a while. Some weeks half the swimmers are ready to move on while the other half need to take things at a slower pace. When the teacher is able to be guided by the class, all needs can be accommodated.
If I had to break the fundamental swimming skills down to fit my planner and slot neatly into a set number of weeks, things would feel stilted, gimmicky and artificial - having the freedom gives my classes the time they need to really get to grips with a new skill or enjoy an old favourite and tailor my teaching to the group. My planner is a huge sheet of A3, full of progressive skills and different song ideas and covered in scribbles to show where we've got to and what we're aiming for next.
If you're choosing a swim school for your baby or child, don't be afraid to ask the teachers how lessons are planned. Learning to swim is far from a linear process (especially for babies and children) and they need to be free to take a step sideways or even backwards as they progress forwards.