This report explores the conditions under which middle-school teachers in New York City leave their schools, and the consequences of this turnover. The focus on middle schools stems from the widely-held view that the middle grades are a critical turning point in the lives of children, and that many New York City school children lose academic momentum in these grades, setting them on trajectories of failure as they move towards high school and life beyond it. This report is based on a survey of more than 4,000 full-time middle school teachers working in 125 of the nearly 200 middle schools in New York City serving children in grades six through eight in the 2009-10 school year. The participating teachers reported whether they had considered leaving their current school or leaving teaching during that school year, and the reasons that they considered leaving. The report links their responses to teachers' reports about their own backgrounds and experiences, to the demographic characteristics of the schools in which they teach, and to the collective perceptions of all of the teachers in a school about that school as a workplace. This report is part of a three-year, mixed-methods study of teacher turnover in New York City middle schools.