Maybe some kind of simple programming language elementary dealing with turtles? A command based system where you tell it to go 5 spaces, draw a line and turn and have the students predict where it goes?
Seriously, high-school= C. Maybe stripped down without any of that pointer stuff or, make that a separate class, and that covers the basic syntax of every other major language out there. I learned fucking pascal off a Mac LC and it nearly failed me in programming 101 in college cause no one used that stuff. But elementary students who can't spell and you want to teach algebra? Go with Logo. I might not remember much about pascal (till recently at-least) but I sure as hell remember spending hours in front of an Apple 2, trying to draw little people, then running them over with my turtle.
And YES. Strip out all that pointer stuff. To pass references, tell students to use &. I KNOW its not in the C spec, but anyone who as ever sat down and actually tried to teach someone programming realizes that people have problems with what a pointer is. I don't know why, but peoples eyes just glaze over. Its a complicated subject especially when you start throwing operator presidence in there like like *ptr++ or *(ptr-4). Those are just the basic examples. If you can get them to comprehend what a references are, then you are half way there.
If you can just get them to sit down and program something because they wanted to and not needed to, then they will learn themselves. Getting to that point is what everyone is trying to do. Just don't try to teach people flavor-of-the-month languages.