The Bill and Melinda Gates Foundation has invested in the development and dissemination of instructional tools to support teachers' incorporation of the Common Core State Standards (CCSS) into their classroom instruction. Math experts have developed formative assessment lessons (FALs) that teachers can incorporate throughout the year's curriculum. The Foundation has asked RFA to study teachers' early adoption of the FALs, focusing particularly on their response to and use of the lessons. The lessons were piloted in urban, rural, and suburban school districts in four states and two national networks of schools during the 2010-11 school year, which is referred to as Year 1 in this booklet. This booklet is a synthesis of what the authors learned from practitioners over the course of the pilot year, 2010-11. It highlights how Math Design Collaborative (MDC) worked in schools and includes what teachers can expect when using the formative assessment lessons (FALs), points out promising practices, as well as teachers' early impressions about MDC's impact on their teaching and student learning.