Creationism and Lamarckianism are two different kettle of fish.
On the law side, Lamarckianism is not a recognized religion.
On the practical side, it is mentioned as a failed hypothesis. Should creationism be taught as a failed hypothesis? I can imagine how well that would go over.
Remember, ID is not necessarily religious in nature ~ e.g. the part of ID that has the mothership deliverying new types of critters from the "new animal factory" in Baghdad on Sandoz 9.
Besides, arguing that "religion" should be prohibited from a class when other fictions are allowed (Lamarckianism) runs afoul of the "free speech" clause in the First Amendment.
You have to be very careful what arguments you advance in support of an "evolution only" curriculum.