I had somebody show me this trick yesterday at a training session I ran.
I’ve played with the control toolbar in Excel and Word, but never had a reason to investigate it in PowerPoint.
This technique does rely on you having YouTube access at the time you do your presentation. It doesn’t physically embed the YouTube video into the file, just makes it part of the presentation. I’d still suggest looking into YouTube downloaders to get the file if access to YouTube in school may be an issue.
As an aside, If your school uses Channel 4 Clipbank to host videos in-school, then you can use a similar technique to link to the videos. This guide shows you how to do that.