You can charge students by the month when you create the session as "monthly recurring". You will be asked for the start and end dates for a monthly recurring class, and families can enroll any time within those dates. You can make the end date up to two years after the start date.
This option will let families select a start date when they register. Then they will be charged each month on start date selected by the family. This screen shows what the family sees when they register. Note that there will not be an end date.
The family's credit card will be charged every month. You can cancel or pause the monthly enrollment on your Registrations page.
This option can be used for online or in-person sessions.