Have you ever tried to teach programming to a newbie?
Arghh..., well, now I do and I hate when they yawn. When my brain is working on 100%, when I'm trying to explain something with the hope that they understand what I'm talking about and they just ... YAWN!

Yawning doesn't always mean they are bored, give him some water, or something to eat. They don't have any control over it.

Teaches Networking/CCNA. Can confirm most are either dumb or ignorant. Sometimes both. Sometimes I keep wondering why they even bother to undertake a college degree. For the paper that says "degree" i guess.

You should have them move around the room periodically. Ask questions that catch them off guard when they start to lose their attention span. It's a natural reaction once the brain has already ingested a lot of information to stop paying attention. It doesn't always mean people are being lazy.

Yawning could also be a sign that the person is getting tired as you are overloading the person with information.

If you are in a position to go outside and get some fresh air. Do it! As in most cases we just need some extra oxygen.