Step 1:
Go to the school calendar.

Step 2:
Filter the calendar to your needs.

Step 3:
Tap and hold the "Subscribe" link.

Step 4:
Press "Copy."

Step 5:
Go to "Settings" on your phone.

Step 6:
Press "Mail, Contacts, Calendars...."

Step 7:
Press "Add Account."

Step 8:
Press "Other."

Step 9:
Press "Add Subscribed Calendar."

Step 10:
Paste the copied link.

Step 11:
Press Save

Step 12:
Go to the Calendar app on your phone & all the subscribed Hilldale events should be synced!