What would be reasonable to include in an Introduction to AI class for a 7th-8th grade after school program? The class meets just 8 times for 2.5 hours weekly, aimed at 7-8th graders with very basic programming skills.  Possibilities off the top of my head: computer learning (neural nets and/or genetic algorithms), constraint/logic based programming (well, it came out of AI, right?), a Brief History of AI, and/or basic game states and alpha-beta pruning.  

I probably can't fit it all in, and I don't want to make it so difficult as to be discouraging.
I don't have a lot of insight into your overall problem, but there is a resource you might consider. 

There is a simple game, The French Military Game, in which a person plays against the computer. The totality of game information is small enough that the computer can remember every position in every game played, so it doesn't make the same mistakes in subsequent games. While it is a known win for the human player, after 6 or so plays it is very difficult to beat the computer. 

The game is available (Java) in a couple of forms at the Greenroom, a place for educators using Greenfoot. Membership is open to any interested teacher.

The FMG once appeared in Creative Computing, now defunct, as an Apple II BASIC game. It uses a bit of math, but ok at the level you are interested in. 

It is, at best, a simple, even naive, introduction to machine learning.  

Disclaimer: I'm not associated with Greenfoot or the Greenroom. 



The game is also discussed with code in Beyond Karel J Robot though that book probably isn't a good resource for your class. 

Another user here (@Ben_I.) points to an applet version with a brief explanation of the game.