Agreed. I taught a similar course here in the US, and I taught binary/octal/hex math, understanding packet flow, how to take apart and rebuild a computer, etc. Don't make this so abstract that there is no physical reality to it all - not all 9th graders think very abstractly. And don't forget HTML, which is at least fun to play with. Floating point (if they have the math background) and sorts are nice, too, for getting a sense of how computers operate.

Don't overlook your local library. Many carry textbooks and have homework clubs or even on-line homework help. Find out who runs the math part of the homework club and ask for help/advice.