This relates to the YouTube for school feature in the Web Security Service.
Google has decided to stop supporting YouTube for Schools effective July 1, 2016. As a result of this this option is no longer functioning as expected.
Official release from Google:
“YouTube for Schools will be turned down on July 1, 2016. We are offering current YouTube for Schools users and all Google Apps users a new way restrict YouTube content with YouTube settings configurable in Google Apps for Work, Education, and Government. Non-profit educational institutions can sign up for free access to Google Apps for Education. If you choose not to use Apps for Education, you can still choose restrict YouTube on your network”
Schools and other establishments that use Google Apps for Education have extra control of YouTube which they can deploy to users logged into their Google Apps account. See the following for more information: https://support.google.com/a/answer/6212415?visit_id=1-636096406727584559-2856952965&hl=en&rd=1