With my DD8, in school we don't really have any control. The kids get what they want in the school library and nobody guides them. By 3rd grade the kids whose parents have an opinion have figured out just not to bring those books home, they read them during silent reading time and just don't tell their parents.
DD mostly wants read what the other kids are reading in school so she can be part of the conversation. It's all the usual suspects. We just let her, as long as she reads other stuff at home.
At home I just ask that she reads books that are more classic, where she can learn more words, be exposed to different dialects, maybe about a different time period, and she does continue with some sort of passionate subject matter like she did when she was little, this winter it's been history.
I agree with what ultramarina said above about the older kids books. I go to used book stores or the library. There are different sites to give lists of them or if you were a reader when you were a kid (depending upon your age lol) there might be some ideas there.
I have DD periodically read out loud to listen to her because as the year goes along her expression/fluency goes way down, it's actually very distressing to listen to her. In the summer she gains again and sounds really expressive etc.
But the grade level thing, I don't really think you can focus too much on that. The teachers just rattle off lexiles and letters of the alphabet, but it never translates into tailor anything for her anyway.
IMHO it's important to make sure some things they are reading are moving them along and talk to them about it so you're sure they understand what they're reading.
