Never miss an important phone call when Do Not Disturb or Silent is set on your iPhone. iOS 10 has added Emergency Bypass - located under each individual contacts - that enables you to choose which calls, emails or texts are allowed through. This is a great way to silent your device at school while still allowing emergency contacts (such as your immediate family) to come through.
iaccessibility shares instructions on how to enable Emergency Bypass.
Note: In early iOS versions, adding a contact to Favorites enabled calls and emails from contacts in Favorites to come through.