Teachers mat leave ends all year round just like other professions. I have lots of teachers and they tend to look for care when their mat leave ends. Only time teachers look over summer for September is if that is when their mat leave ends or if they moved house over summer, just like everyone else who changes carer. They not tend to seek new carer based on moving schools but instead on their home location.
There not usually a big influx of interest over summer from teachers. They is lot of interest from parent seeking before after school care esp if in younger grades because lot of parent delay moving until Summer months so not to disrupt school life. Also parents new to school area or whose children are just start school looking for before and after school care.