Call me a complete geek, but I love to diagram sentences! We started doing this in sixth grade, and I found out I had a knack for it. I think learning diagramming early helps students learn how the parts of speech function in a sentence and this helps them learn better grammar.
My "basic" grammar class in college was a doozy. Everyone had to keep a diagramming notebook and bring it to every class, along with a ruler and two pencils. It was a small class and every student had to diagram a sentence on the board every day for class credit.
Needless to say, I learned grammar and diagramming in a hurry! That knowledge has served me well in my adult life.