If it's a good class, they will have guest speakers and it won't all be just a couple of guys all day long. It's a good place to watch how things are taught as well as what is taught.
Try to glean as much as you can from the teaching style and what you like and what you might do differently.
Don't be afraid to ask questions about everything, even their teaching style. I'm not saying call them on it if you think they are wrong but maybe ask why they did it this way instead of another. Compliment from the audience, if you don't like something, pull them aside during range time or something.
Remember you may be the first person a lot of people will learn their first lesson on guns, so learn to teach, not just instruct.
KK