I know a lot of people who feel there is no value in diagramming. I, on the other hand, use it frequently, both in writing and even occasionally in reading. (It is really helpful to me in finding antecedents, figuring out what clauses are subordinate, the relationships between sentence elements–I do it often when reading scripture or eighteenth-century writing.) I also use diagramming often in my writing, when I have a sentence that is particularly difficult, that I just cannot get to say what I mean, when I am struggling with how to connect two or more ideas. I love diagramming and have been known to diagram sentences during class and speeches just to keep myself awake.
Why the wildly divergent opinions? I’m not sure. It might be a learning-style issue, actually. Some visual learners, especially those that really identify with maps, graphs, etc., may really benefit from diagramming. Very analytical thinkers, those who need all the details in order, may also benefit. And, since diagramming, at least basic diagramming, is really easy to teach, it seems worthwhile to me. OF my two older sons, one likes diagramming as a tool, and one does not. I would not have known which one was which originally, however. Diagramming gives a way to “see” the grammar concepts, and it’s like a puzzle. The son of mine who likes diagramming is a puzzle-nut; he does logic puzzles and things like that for fun. I haven’t caught him diagramming me while I speak yet, but he might do it to others, I don’t know. I know he’s seen me do it and thinks it’s hilarious.
So, yes, I see value in diagramming, and I do use it to help me with my sentences. I make my kids diagram awkward sentences when they write. I must confess I’m the only person I know who does that, to be fair to the anti-diagramming crew. But it’s so easy and fun to teach. And it might be helpful to some of your children. You might even have a nutcase like me in your bunch. In which, by all means, teach her to diagram so she can make sense! LOL If you teach it to a child who does not use it much as a tool, not much is lost–they’ll still have that understanding of how sentence parts relate to each other.
One other note–diagramming is one of those things that can break down the English speaker’s resistance to the idea that word order is all important. Obviously it’s not. When you have to take those introductory opening clauses and stick them somewhere else BESIDES the first line of the diagram, I think you begin to see that word order is often arbitrary and this can be very useful in foreign language learning. We often diagram English sentences before translating them into Latin. Of course, apparently I’m an outlier.