This debate is painful to watch. In a way both sides are right, and both completely wrong. They miss the point.
The official curriculum offers evolutionary biology as a description of the way biological systems operate and change. The unofficial curriculum provides the never-discussed claim that the physical description of a system tells you everything you need to know: that "how" is the only important question and that "why" is irrelevant.
The combination of these two features, the scientific analysis and the undebated philosophical principle, form a powerful argument against Christianity (or Islam, or ...): if you have a physical description and if the physical description is all that matters, you do not need the "hypothesis of God."
Rather than attack the underlying philosophical flaw, the ID folks want to offer design as a description of a process. That's a joke. Their motives seem good enough (to try to combat the atheist doctrines children are taught), but they miss the point entirely.
What I'd do (what I do with my own children) is explain that process and purpose aren't the same thing. (This wouldn't be a science class, but a short series of classes on philosophy.) You would use evolution as an example, or the baking of a birthday cake: just think of describing all the chemical processes involved--you can make cooking sound terribly deterministic.
It is perfectly true that philosophers don't agree about these sorts of things, but we never bother to explain to our youth that there even is a debate about meaning; we just feed them the reductionist line. (I decline to get into an argument about whether this is deliberate or not, I merely note the fact.)
Then all you need to do in science class (and history class, and ...) is remind the students of what they learned about meaning, and forge ahead with the usual class.