The teachers, of course, had to teach this sort of stuff. Truth to tell, very bright fourth graders might be able to master it (as long as no algebra involved).
I think that the math on this test would have been easier for a bright fourth grader than the language.
Some of those language concepts are difficult for anyone. I don’t know any fourth graders who would grasp the idea that an adjective can sometimes be a noun in that sentence that had to be diagramed.