Using the hour this way is the best route for kids who can already swim and are at the point where endurance work requires covering some serious distance.
It also is a great length of time for adults learning to swim. It allows for the pace to be adjusted to that whatever we are working on is building a rhythm.
Younger children alone tend to struggle with focus or getting to tired to be productive in this class. If it is only one child we will need to play some games in the middle just to bring them back to a point they can focus and have the energy to do the tasks at hand.
Kids who require things to move at their own pace one-one-one may do very well with this structure.
It is an excellent way to work on short-term goals quick like getting ready for a season or event.