There are also the MTH "Research Guides" that are non-fiction companions to the stories.
I read all the books to DS before he was independently reading and we loved them. Such a great way to introduce different historical and other non-fiction topics that we could explore further. I remember we read the one where they meet Louis Armstrong in New Orleans and I went online and found some recordings of his music to listen to.
Even now that he has graduated to higher level books, we still look forward to the new books coming out.
