The concept of an intelligent designer shouldn't just be dismissed out of hand — to do so would be simply telling students to accept what the teacher tells them on faith, while rejecting what their religious leaders are telling them to accept on faith. If ID is treated as just another hypothesis — then you can proceed to disprove it, in a scientific manner.
ID is not scientific evidence — no more than the ToE is evidence. Observations can be evidence — and there are many things that both ID and ToE proponents observe including: the existence of a multitude of species; the complexity of multicellular creatures; the complexity of a single cell; etc.
Darwin himself made such observations. He then formulated a tentative theory that explained his observations. He (and a great many other scientists) then used the theory to generate testable hypothesis. So far, the hypotheses have not been rejected, and the validity of the ToE has increased accordingly.
Why not follow the same process with ID, and show — scientifically — how that “theory” has been disproven?
There is a problem when you are trying to apply science to the supernatural. And ID is about applying a supernatural explanation for "design" (i.e., everything).
Anything can be explained if all you need to do is assume the supernatural. And that explanation thus becomes meaningless, leading nowhere.
There are still major unknowns in the theory of gravity. Saying Goddidit does not help to explain those unknowns. Rather, it tends to prevent the research. Why do science if all questions are answered by Goddidit?