From the Guardian:
Children's writers relish using language well; of course they do, that is an essential tool of their work. Spelling, punctuation, regular and irregular verbs and everything else about grammar underpin all that they do. (It is odd that anyone thinks it doesn't.)
None of my elementary schooling involved diagramming sentences or anything of the like. That I remember, anyway. I do remember, though, very clearly, that in second grade, our classroom teacher made little grammar books* for each of us, and every time we did something NEW and DIFFERENT (and CORRECT) in an assignment, she would chronicle it in that book. (She was VERY LIBERAL with the foil stars, bless her.)
I also very clearly remember her astonishment when I used a serial comma without any sort of prompting—she asked me how I knew to use it, and all I could tell her was that "it looked right". But now, of course, I assume it must have come from reading.
*The covers were made from wallpaper samples.