When videos are restricted or it shows a message like this:"This video is restricted. Try signing in with a Google Apps account" it means that your internet network or your google apps domain has a filter for YouTube videos. To solve this please follow these steps:
- Visit YouTube page
- Check if you are logged in with your school account (do so if not)
- Scroll all the way down and see if you see this:
"Restricted Mode" is probably ON for you, if you can, switch it off. Sometimes the button is blocked and you as a teacher don't have control over it -- that means that your school/district has enabled this.