I agree the merits or demerits of Intelligent Design (or for that matter Probabilistic Design) can not be rationally or even adequately discussed at the middle school or high school level. In general teachers at these levels are too poorly trained in science to do any more then rote teach facts out of a textbook. That's a hard enough problem considering how bad textbooks are at that level.
You're right about how bad textbooks are. As I understand it, some biology textbooks STILL present fake "evidence" for Darwinism, e.g. Ernst Haeckel's fake embryos, and the fraudulent peppered moth photos!
But I have to disagree with you about the need to wait until the college level before students can have an intelligent discussion about intelligent design.
Smart high school students deserve more than a Darwinian indoctrination; and regardless of how ill-trained their teachers may be, I believe there are resources out there that could be used as a basis for discussion of the subject.
One is a short, easy-to-read book by James Perloff called The Case Against Darwin: Why the Evidence Should Be Examined.
The book is a good overview of the subject; it also exposes some Darwinian claims, e.g. Haeckel's embryos, as a fraud.
Just so. I'm sure there are lots of very good high school science teachers. There are also far too many, from what I have read, who teach science without having been science majors. I sincerely wonder what percentage of high school biology teachers can do justice to the teaching of evolution.