Check out View Pure:
Once your video has been "purified", it'll open up in a new window with no ads, suggested videos, or comments!
Here's a pro tip. On the www.viewpure.com main screen, you can also drag the big orange button button that says "Purify" up to your bookmarks bar in Chrome:
Then, anytime you're on Youtube and you want to show it your students the video in "Viewpure", all you have to do is just click the button on your bookmarks bar and it instantly changes!