Realistically speaking: scripting languages (Score 1)

Outside of IB courses, and wannabe game developers on their own time, high school students shouldn't be subjected to languages like Java or Python (and god forbid C or C++). I teach Java at a university, and even at that level... I miss Pascal, which happens to be what I learned in high school.

A good start might be hand-written HTML with some Dynamic HTML or other JavaScript starting about mid-year. HTML gives them an introduction to the basic ideas of programming, like commands in text, syntax, nesting, comments, and the write-(no compile)-run cycle before they get to the real thing. They should use the W3C Validator from the start, to teach the concepts of well-formed code in a very forgiving environment. Then move on to JavaScript to teach them all the usual constructs.

Another good choice (mentioned elsewhere) would be some other kind of scripting environment. If your school has the cash, Flash would do the trick. Or a scripting language attached to a game engine. Something with immediate results. Kids just aren't as thrilled with Hello, World! as they used to be.

In either case, they end up with something they can show off. Nice way to get them interested in programming without scaring them off, and still teach them the basic techniques. And hopefully they'll end up in my classes, because handing out all those A+s would make me look good.