What age reader will enjoy "The Side Ways?"
I've been getting this question a lot. So I figured a post wouldn't hurt.
Short answer: it's intended to be appropriate as a YA (Young Adult) book in terms of content. In terms of vocabulary, it's going to be on the older side. It's not meant to be difficult... but I mostly use the vocabulary that I'm comfortable with telling a story, and so I don't specifically alter word-choice for specific grades-or-below.
In my mind, as I wrote, the book was always being read by someone very similar to Kendra, the main character: a clever, precocious 15-year-old.
Since it's fantasy, a couple parents have basically asked, "If my kid can read the 'Harry Potter' books, will they do OK with these?" The answer is yes. If your kid can read Harry and enjoys those books and you're OK with the levels of peril, violence and grown-up situations covered in those wonderful books... they'll do fine.
There is peril, sometimes mortal. There is violence, sometimes deadly. There are some scary things, but not intentionally "horror" things.
There is no sex and no romance and there won't be. I'm not a prude by any stretch, but these aren't books about romantic relationships. They're books about the possible end of the world. There may be some light flirting at times or reference to relationships... but it's not ever going to be a "thing" in the series.
Hope that helps! I'm especially interested in what young (12-16) readers think about the series... so please feel free to ask your kids to review the book(s) and/or contact me.