The selection of your swim school should be based on a number of factors, but most importantly, on the quality of teaching. If you can, find out about the background of the swimming teachers; do they have appropriate qualifications? (look for AUSTSWIM or InstyleSwimming certification in Australia) Do they have experience of teaching your age group? Ideally they should aim to be completely transparent about their teachers' credentials and encourage parents to find out more about their teacher's experience before they book you into lessons.
When arranging lessons its also worth checking the size of the classes. Remember, if there are 6 children in the half hour class, you can't expect to have more than 5 minutes of one-on-one teaching time. If you feel your child would benefit from more personal care consider searching out private or small group swimming lessons with a company such as http://ActiveUnlimited.com. Our experience has shown that the investment in smaller group lessons has a significant impact on the speed that children learn.
If you have a pool or a friend or relative with a pool, consider learning to swim there with a private swimming teacher. It's convenient, and children often respond much better to a teacher when they feel confident in their own home environment. The additional benefit is that the teacher can enforce your 'Rules of the Pool' and include a focus on safety.
Parents often find it tricky to fit swim lessons into childrens already busy schedules. Swim schools at public pools have regimented schedules, but don't be tempted to put your child into the wrong level if it's the only time you can get to the swimming pool. A level too low and boredom will soon set in, and a level too high will become frustrating. The advantage of learning to swim at home is that the swimming lessons can fit around your schedule and adapt to the exact level your child is at and progress at a speed that is right for them.
Finding the right swimming teacher and the right swimming lessons are important to your child's ongoing enjoyment of the water. It's worth doing your homework and considering the options before diving in.