A great idea for Grammar

I was in the library reading through some issues of Homeschooling Today Magazine. I’m not sure which issue this was in.   I thought this was a great idea for Grammar. 

The mom who wrote the article said that a friend gave her the idea to buy a good 12th grade level grammar book for each child, but do a little bit each year from it starting in 6th grade, slowly working your way through the book over the course of 6 years. Unfortunately, she did not give any examples of titles, however.

I really liked this idea because it is CM friendly, assuming that grammar is a finite body of knowledge, that can be mastered and worked through only once.

I’ve already purchased AG for the fall. Thankfully I found it used, but since it is so expensive I am using only 1 copy for my 3 oldest children, and we’ll be using page protectors and writing on those instead of writing in the book. But if I could find a great grammar book that would work for this idea, I’d be open to trying it with my son who is starting 6th grade in the fall.

Any ideas?

Nanci