Anyone interested in mathematics teaching and learning is likely to get hooked on case discussions. Barnett, Goldenstein, and Jackson have found that teachers gain a deeper understanding of mathematical ideas themselves in the process of examining the mathematical thinking of children. Their case discussion approach promotes dialogue between and among teachers which serves as a catalyst for changing and improving the curriculum. Case methods open a whole new way of fostering teacher learning that both draws on and informs practice. The cases-written by upper-elementary and middle school teachers about their experiences covering fractions, decimals, ratios, and percents-enhance professional development by stimulating reflection and dialogue about problems encountered in the classroom. Although the cases contain many examples of teaching that reflect the NCTM" Standards," they carry no presumption that the teaching portrayed is either "good" or "bad." The accompanying "Facilitator's Discussion Guide" provides many practical suggestions for initiating and leading case discussion groups.