I would like to encourage you to do this. I'm an Engineer but I've taught everything from University level Electronics, to IBM Engineers, to MiddleSchool Robotics (my favorite) to Kindergarden Computer Demolition, and it's one of the most rewarding things to do.
I hope I can help in some way. See stuff on the ArduinoInfo WIKI here - http://arduinoinfo.info
I have some starter stuff there like:http://arduino-info.wikispaces.com/Arduino-What-IS-it
I have provided Starter Kits to several schools and Universities and gotten good feedback from many teachers. I'll be happy to give you the 10% Educational discount I give to schools. So $29 for a Starter Kit with a good Arduino compatible, many kinds of input and output devices including a servo and a 2-relay board.
A key point is for students to own and take away their starter kit, and not have things stop at the end of the class.
If you find some kid who's really into this and doesn't have the money, email me about it and I'll give you a kit for him/her.
Look over the YourDuinoStarter pages and see if you feel it's at the right level. I don't feel you need to dig too deeply into Electronics, Ohms Law etc. at the beginning. The questions will come and those students who are engaged and want to be able to do things on their own will dig deeper.
Let us know how it goes and what you end up doing...