It is a truth universally acknowledged that teens read up. Your protagonist should be a couple of years older than your audience, or so the thinking goes. It's time to start questioning this assertion, at least when it comes to high school students.
I'm surprised how many times I'm asked what aged audience I was thinking of when I wrote Secrets of Truth & Beauty. Occasionally a parent or teacher has told me, a bit guiltily, that they liked the book but wouldn't give it to their fifth grader. That's fine, I think, I didn't write it for your fifth grader. I wrote it for high school students.
In my job as a high school librarian, I help teens to make their reading choices every day. For the most part, they want to read about other teenagers. When I look at the fiction on my return cart, I do not see a row of adult novels. Instead I see mostly YA, with a few Jodi Picoult and Stephen King thrown in – authors, it should be noted, who often feature teen characters.
It would be a reasonable assumption to think that since I am a YA author, I would be inclined to purchase and recommend YA books. However, my evidence is not simply anecdotal. Every year, librarian Jo Lewis asks members of LM-Net, a school librarian list-serv, to report their top ten checkouts. She collects and analyzes the data, and compiles lists for each type of school (elementary, middle, secondary). If you go to the list, and choose "secondary" from the drop down menu, you'll see that the top ten for high school students are all young adult novels.
So that's high school. What about younger teens? In 2009, the Twilight series was tops in middle schools as well as high schools – no surprise there. With a few notable exceptions (The Lovely Bones!?), the rest of the top ten are books with a middle school audience in mind. While it seems that younger teens may range both younger and older, they too, are eager to read stories about kids their age. Teens it seems, want to read about teens.
Thankfully the explosion in YA literature means that there are books for every age and interest. For me this is not simply a matter of curiosity, but one of equity. Teens, like everyone else deserve to see themselves in books. Sixteen, seventeen, and eighteen year olds shouldn't be forced to read about mid-life angst since the younger kids are reading about their lives.
As writers it's our responsibility to portray our world's honestly. If the stories we tell about teens also find resonance with a fifth grader, so much the better, but we needn't simplify or clean up because this younger reader might pick up the book. Write your story. Write the truth. Everyone will be better off for it.