Four fourth-grade teachers are bent over a conference table, chins in palms, concentrating on one student's assessment paper. This paper is one of many on the table, organized into several ragged piles. The teachers are discussing nuances of the student's work, trying to reach agreement on the quality of the response. The goal of this careful analysis of student work is to better understand how thoroughly students have learned the science concepts taught. To achieve this goal the teachers are engaging in a sophisticated professional development activity: moderation of student work in a study group. Moderation is an interactive analysis of student work used by small groups of teachers to qualify student understanding and increase teacher sensitivity to student progress with difficult, complex concepts. Moderation is used to make apparent the relationship between instruction and learning. Moderation orientation and procedures are discussed in this article. A list of 7 resources concludes the article.