H.W.
I don't know if I can help in the way you like-- my son is six and loves those books, but he also adores Captain Underpants, Frankenstein and we are devouring an adaptation of Beowulf right now. Scatological humor and horror.
Oh, how about the Teacher from the Black Lagoon books by Mike Thaler? He also does a Class from the Black Lagoon chapter book series. Kiddo loves those!