1. First login to the School app at Schoolname.myschoolapp.com
  2. Click the Menu button (3 horizontal lines.)
  3. Click Calendar
  4. Click Options
  5. Click Webcal Feed
  6. To add filters such as for Athletics:
    1. Click Individual Filter Feeds
    2. Click the Gear icon next to the Calendar
    3. Select which options to include in the feed
    4. Click Save
    5. Repeat steps 4 and 5 to reopen the WebCal Feeds
  7. Click and hold on the names of one of the Calendars
  8. Copy the Link Address (Webcal)
Then on a Apple Device navigate to:
  1. Settings
  2. Click Mail, Contacts and Calendars, 
  3. Click "Add Account."
  4. On the list of account types, click Other at the bottom
  5. Click Add Subscribed Calendar
  6. Press and hold in the text field to paste in the iCal feed URL that you previously saved to your clipboard, and click Next

Your device will verify the feed URL and add it to your calendar. Subsequently, new events will automatically populate
in the Calendar app.

If you need to add your Calendar to a Android Device or Google Calendar follow the steps in this link:

How can I open the calendar feed in Google Calendar?