Gosh, I wish I had my old CORE books from HS that I could share with you.
Basically, it was structured writing in 5-sentence blocks. A paragraph would be written with the writing style you were to mimic underlined and explained after the sentence. The object was to write a 5-sentence paragraph, paralleling these concepts. It was hard sometimes, but I'm a better writer because of that. It was 4-years worth of this type of learning. It was developed by one of the English teachers at the time.
To better understand how it was structured, the first sentence might want you to use a participial phrase. The second might be parallel structure. The third might want a demonstrative in it, etc.
I don't know if there are any books that you can order that would use this type of structured writing. I hated it in HS, but think it was truly the best way to teach writing.