Clarification on my Swim (non)Sessions

During the school year, I run my swim program a bit differently than other local programs. The truth is I don't actually have "sessions".
Once a child is placed in my program, he/she stays in a chosen spot until one of two things happen:
the child graduates out of my yurt pool program and transitions with me to the aquatic center or the family decides to exit my program.
The frustration of a child "not getting into the next session" is the main reason I don't like sessions. The downside is that I don't have a lot of openings, as most people tend to stay until their child learns to swim!
I run classes on a month to month basis. Parents are billed at the beginning of the month and charged according to how many weeks are in that month.
The exception to my non sessions is during the Summer. Many families are traveling during this time, so I create mini classes to accommodate busy schedules.