Good question. It was our experience that once the student could read aloud More New Friends without help, he was adequately prepared to read his own school books in history and other subjects around fourth grade and up.
At the end of More New Friends we felt we had reached our goal in getting him to that fourth-grade level. From there out he could integrate his continued growth in reading with his other subjects that used living books and narration.
The narrations would help us evaluate his reading comprehension as he progressed to harder and harder books, but he wouldn’t need separate lessons focused only on practicing reading.