Hey okky.
The Sound Reinforcement Handbook will make their eyes glaze over, and has a lot of stuff in it they don't need to know. It's great to have for a reference, but I strongly recommend The Guide to Sound Systems for Worship (ISBN 0-79350-029-X) for $25.00. It's also published by Yamaha, it's only about half as thick, much clearer and easier to read, and has a much more thorough index.
Also, I have some old speakers and guitar pickups that I've dismantled so I can show them when I'm explaining how things work. I put a small amp on a table, connect a speaker to the input (alligator clips to 1/4-inch jack) for a microphone, same thing for the output, then thump on the (microphone )speaker or talk into it, induce a little feedback, etc. Replace the microphone with a guitar pickup and play a little guitar string over it (you'll have to build a little guitar). It's very hands-on, and they love to play with the little guitar. This helps them understand the signal chain which is useful for simple troubleshooting.
We talk about harmonics, instrument timbre, energy of different frequencies (low notes on a piano only need one string, middle notes need two strings, higher notes need three strings), how much more easily low frequencies (pitches) travel through air (nearby lighting strike versus lightning strike miles away, what do you hear most from the loud party down the street), so that they can consider instrument harmonics (timbre) and the difficulty of high frequencies traveling through air when making EQ decisions.
I show them how the mics are labled, where they plug into the snake, where the snake plugs into the mixer, output to amplifier, cabling to speakers. All of this happens before I let them sit down at the mixer. I'm convinced that sound techs that start learning at the mixer never get a good feel for the signal chain, adding mics, troubleshooting, etc.
Good luck!
