A few I've come across are these. I'm sure you know others.
Most are books whose main characters are thirteen or fourteen, older than typical MG main characters but younger than most YA main characters. Some of them explore issues that may be tough for middle graders (abuse in Okay for Now, a sister who died in a terrorist bombing and a drunken dad in My Sister Lives on the Mantlepiece, and dating relationships in many). And the storyline of each is elevated above the normal middle grade book.
So, what to do?
The librarian at my local library houses each of these books in the YA section, all except The False Prince. The Cabinet of Earths moves around; I've spotted it in both the MG and the YA section. So maybe the librarian is trying to figure this whole thing out too. The covers of these books may draw a middle grade audience more so than a YA one. And what's under these covers is somewhere between MG and YA.
So, my knowledgeable blog readers, solve the conundrum. Where do books like these fit? Do they need a label all their own? Often they're called upper middle grade books, but YA readers may ignore them just because anything determined middle grade is, in their minds, for kids. Hmmm. It's worth discussing. What's your take? And what other books fit this conundrum?