This article examines a 1-month US-based teacher training/development program for Mexican teachers of English. Three sets of survey data were collected from 20 teachers—on the first day of the program, the last day of the program, and 6 weeks after the teachers returned to their classrooms. Feedback and assessments from program trainers were also examined. The data suggest that there were important changes in teachers’ attitudes, perceptions, and behaviors during the course of the 1-month program and that these changes persisted some weeks after the end of the program. The authors conclude by discussing features necessary for effective development programs. These include assessing the needs of the teachers and their schools’ expectations, providing practice opportunities for teaching, and including a language component for the teachers.