Here's how to download a YouTube video so that you can show it in class from your computer, flash drive, external hard drive, etc. You will probably have to find your video clips on YouTube at home, download them, and bring them to school on a portable drive. If you already know the link that you want to use, you should be able to convert and download from anywhere.
Go to http://youtubeinmp4.com/
Paste the link of the YouTube video in the box
Click on "Download MP4"
Click on the "Download MP4" directly under the video image. Note: There are usually other buttons that say "Download" or "Play Now" - don't click those because they are ads!