My computer informs me that today is the birthday of Gertrude Chandler Warner. Aside from having a tremendously fantastic name, Ms. Warner has the distinction of authoring The Boxcar Children (and at least 19 sequels, to which more than 130 have been added by ghost-writers). I'm pretty sure that I have read more Boxcar books than any other series, except for maybe...dare I admit it...The Babysitter's Club. C'mon, at least it wasn't Sweet Valley High.
I distinctly remember picking out the latest Boxcar Children book from the Scholastic book fair each year, although I think they were still publishing Werner's originals--the first ghost-written title (#20) didn't come out until after I had moved on to more mature reading (like Spider-man comics).
Nowadays, we have all sorts of advanced reading metrics--Scholastic's site states that The Boxcar Children is a Lexile framework 490L, Guided Reading Level O, appropriate for grade level 3.2 (2nd month of 3rd grade) and children ages 8-10. Back then, all we cared about was the number in the top-right corner.
Which brings us to tonight's truism: If you have written enough books that your titles simply become numbers, you've probably over-done it. I'm looking at you Hardy Boys and Goosebumps.