We Could Be Brothers by Derrick Barnes.

I have been reading Derrick’s book slowly, but only because I’m savoring it. “We Could Be Brothers” is a really special book, because the story is so sophisticated, but its reading level is about third grade (lexile 600).This book is a treasure for older boys reading below grade level.
Barnes writes the Ruby series as well, which is really enjoyable, but We Could Be Brothers is the real thing. Add this to your classroom libraries.