Custom Recurrence is a Google Workspace Add-on for Google Calendar that allows you to repeat events according to your own repeating patterns. It also supports multiple configurations, so if your school has multiple repeating patterns everyone can still use it.
Think about that standing meeting on A Days, during Period 5. Simply add the first one to Google Calendar, then select that event with the add-on open and choose your recurrence type.
Select Specific Dates - (i.e. Select from a list of A days to repeat.)
Create for Every Other Date - (i.e. Repeat every other A day)
Create Series for All Dates - (i.e. Repeat every A day)
Annual Rollover - (i.e. Repeat on this same Tuesday one year from now)