Essential Understanding Series Books on Algebra
Teachers and administrators appreciate NCTM's Essential Understanding Series because each volume in this series focuses on the big ideas of a specific subject and breaks each challenging topic down into the fundamental concepts that are critical for teachers to understand.
"Developing Essential Understanding of Expressions, Equations, and Functions for Teaching Mathematics in Grades 6–8" is one of three books that focuses on algebra.
The books in this series examine the big ideas and related essential understandings, and allow teachers to focus on the ideas they need to understand thoroughly to teach confidently.
http://www.nctm.org/catalog/productsview.aspx?id=129