I guess one answer is the following: that "academic freedom" (which is one of the motivations for tenure, i.e. it protects one's academic freedom) applies not o

I guess one answer is the following: that "academic freedom" (which is one of the motivations for tenure, i.e. it protects one's academic freedom) applies not only to research but to teaching activities as well... but again, you're right, in that perhaps this makes sense in a university environment (in which curriculums can easily vary in many ways, and still be valid) but not so much in elementary schools, primary schools, high schools, etc, in which a curriculum is more restricted in its scope, and pre-defined using standards, etc.