Sheryn Spencer-Waterman 
Handbook on Differentiated Instruction for Middle & High Schools [PDF ebook] 

This book has an abundance of time-saving, practical strategies for teachers in grades 6-12. A treasury of activities and resources, this book explains, demonstrates, and helps you select among a wide variety of differentiation processes, such as whole class differentiation, tiered lessons, learning centers, flexible grouping, literature circles, individualized instruction, independent study, and learning contracts.