Leprechauns Don't Play Basketball is the fourth Adventures of the Bailey School Kids book and brings a bit of a unique twist to the premise. Whereas most books of the series are fairly straightforward--the kids get a new teacher or other authority figure, spend the book trying to prove and/or disprove that the adult in question is supernatural, and ultimately come to a conclusion that's shaky at best--Leprechauns introduces some world-building (that is unfortunately never seen again, as far as I know). As with most of the series world-building, this has to do with the children's third-grade teacher, Mrs. Jeepers.
Mrs. Jeepers, the teacher from Vampires Don't Wear Polka Dots, takes center stage again in Leprechauns, this time set up as something of a hero opposite the new gym teacher at Bailey Elementary, Mr. O'Grady, a diminutive Irish man whose actions hint that he's actually a leprechaun. As the kids investigate whether there really are such things as leprechauns, they stumble across a myth unique to the Bailey School Kids universe that chronicles an ancient feud between vampires and leprechauns that seems to revolve around a particular green gem... a green gem exactly like the one Mrs. Jeepers wears on her brooch.
It's actually a fairly refreshing change from the series typical style, and I appreciate having Mrs. Jeepers cast in a heroic light for the first time (considering that, as a child reader of the series, I was always fond of her character). Like all the rest of the books, there's no real conclusion to the mystery; a series of very convenient coincidences seems to support the idea that Mr. O'Grady is indeed a leprechaun trying to steal Mrs. Jeepers brooch and possibly kill her, but the kids find no concrete evidence to prove the supernatural.
The series is quite formulaic and understandably juvenile given the audience, but I've always quite enjoyed it. It's not one of my absolute favorites, but it is a fond childhood memory of mine that I'll look to from time to time when I'm craving some nostalgia. The stories are short and simple but entertaining, and I appreciate the "decide for yourself" element of the books; if your kids wants the story to be supernatural, it can be. If they'd rather debunk the idea of the mystical, they can do that, too.
I definitely recommend the series to anyone looking for a new set of chapter books to check out. If you're looking to start reading The Adventures of the Bailey School Kids for the first time, I recommend starting with Vampires Don't Wear Polka Dots; after that, there are only a handful of books that have to be read in order (Dracula Doesn't Drink Lemonade should come before Dracula Doesn't Rock N' Roll and Dracula Doesn't Play Kickball, as an example). Otherwise, it's a series that can be read fairly haphazardly, and I'd personally advocate checking out some of the later books after Vampires Don't Wear Polka Dots to get a glimpse at the quality of writing the series ultimately settled on.