Who is this book for?

When I wrote When Comes Such Another, I envisioned potential readers to range in age from teenagers to adults. The eighth grade students at Portsmouth Middle School who have been reading the book tell me that students younger than they are might struggle some, but I suspect that some sixth and seventh graders could easily manage the concepts in the book. Several adults have read it and liked it. What do you think? What is the range of ages for which the book is appropriate?