ClassroomParent allows you to configure it to sync calendar events based on a ICAL feed. If your school uses Google Sites, you can generate the ICAL feed url following these instructions.
Once you have the link, you can update your ClassroomParent settings to begin to sync upcoming events in your Google Sites calendar to School events in CP.
Once saved, the system will automatically sync all future events. Nightly, the system will check for any updates (additions, changes, and removed events).