Middle school students consolidate their understanding of integers and rational numbers, increasing their facility with fractions, decimals and percents and encountering proportionality. This book shows how students can explore these important ideas in such diverse activities as exchanging currency and using area models to develop algorithms for multiplying and dividing fractions. Underlying each activity is the belief that students learn best when they build computational fluency on a firm conceptual foundation. The supplemental CD-ROM features interactive electronic activities, master copies of activity pages for students and additional readings for teachers. Numbers and the operations that we perform with them are the starting points for all mathematics. Accordingly, Principles and Standards for School Mathematics makes the Number and Operations Standard first among the five Content Standards and gives it a centrality across the mathematics curriculum from prekindergarten through grade 12.