Hi Fred,
It would all depend on the amount of time available.
1) Demos, are you talking about doing pens, probably slimlines. They can be done pretty quickly.
2) Hands on would require insurance, this could be very costly. Depending on the numbers of 7 graders involved, would you have enough time to run them through? As a beginner, probably have to allow minimum of 15 minutes per youth, to get a decent finish with sanding. I know my first pen took me about 1/2 hour, that was without instructions/tuition.
Unless you can get some volunteer penmakers to help, it could be a major problem. I've assisted my Club at several shows, where we just make spinning tops, handing them off to the kids, we are flat out all day, and we have 2 lathes running.
Kryn