I feel compelled to add my own 2c on this discussion. Looked at from the point of view of Bloom's Taxonomy, diagramming sentences is pretty much Analysis, which generally means that students would have already mastered or at least reached the Knowledge, Comprehension, and Application levels within English/Language Arts. I'm not sure most 6th graders (or even 9th graders) have mastered them. This would support the hypothesis, already stated, that the good students do well in diagramming, and they don't really need it!
I've lost track of how we got onto this subject, too, were we talking about the merits of proofs? Where on Bloom's Taxonomy would you place them?
Ben :D ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Ben Dillon (email@example.com) St. Joseph's HS, South Bend, IN "Why, sometimes I've believed as many as six impossible things before breakfast!"