When did Ender's Game start being marketed as YA? As best as I can remember when it first came out, it was just another adult SF book. It wasn't until some years later that I saw it with a different cover being shelved in the YA section, and it struck me as deeply weird.

I mean, it's not like I would forbid a middle-school/junior-high kid under my jurisdiction to read it; but if such a kid were to ask me for suggestions, Ender's Game would not be the first book to come to mind, nor even the 500th book.