When you link to a YouTube video you always get the related videos at the end. This can be a distraction at school.
Next time you click on the Share button you get the video URL choose the Embed option instead. Unselect "Show suggested videos when the video finishes" and then copy the embed code.
It will look something like this:
Next, just copy the URL out of the embed code: http://www.youtube.com/embed/s_21p14TAXM?rel=0
That "rel=0" will make sure that no related videos pop up at the end of the video.
While we are on the topic, it is also worth noting that you can stick any URL in place of the YouTube URL in those embed codes. I use them whenever I need to embed a site or page element into my blog. Simply adjust the height and width to fit your needs.
Finally, try right clicking on a youtube video and select the "Pop Out" feature.