We diagrammed at least a gazillion sentences ...
I always hated it, but I did learn to write a cogent sentence.
And you think that parsing sentences helped you do that, Joe, learn to write a cogent sentence?
As I've mentioned to Pom many a time, you [and every other child] knew how to parse a sentence by the time you were five years old. You just didn't know the artificial names given to the parts of speech, but you sure as hell already knew the parts of speech.