I must admit that I cannot take credit for figuring all this out. That honor goes to Dr. Francis Christensen, who was a professor at the University of Southern California. In 1967 he published his masterpiece, The Christensen Rhetoric Program, which proved beyond a doubt that the study of the basic grammatical building blocks—phrases and clauses—is the fastest and most effective path to better writing. Christensen’s most important discovery was the amazing numbering system that graphically shows how those phrases and clauses accumulate outside of the main clause, leading to an almost infinite variety of sentence structures in what is ultimately known as style.
In 1988 I acquired the copyright to the works of Dr. Christensen, and since then I have revised his original text and written an additional pair of workbooks, resulting in a three-book series, published as The Stewart English Program, that spans grades seven through twelve. I have also reprinted Christensen’s collected essays, called Notes Toward A New Rhetoric: Nine Essays For Teachers. Amazon has them all. (from the about page at Strata Writing)
If you a fan of the work of Francis Christensen, click on the above hyperlinked text. Don Stewart is carrying on Chrstensen's work.