I'm very late with this but perhaps for future reference. What about Freak the Mighty, it has a lexile of 1000. From School Library Journal: "Max has been taunted all of his life as stupid and slow. When he meets Kevin, a tiny Einstein in leg braces, they defend the weak, right every wrong, and solve the mystery of Max's past.
You can give the METATRON books a try. Great read for middle grade students. No extreme violence or vulgar.
Sincerely,
Laurence
www.laurencestjohn.com