This investigation examined how middle school teachers implemented Word Generation, a cross-content vocabulary intervention and how the program affected student learning of academic vocabulary words. Participants included four content area teachers and their sixth-grade students. Students received vocabulary instruction in their social studies, science, and math classes. Results of the posttests revealed that students showed positive differences in their learning as compared with a comparison school and maintained those differences on a delayed posttest. In addition, teachers' sensemaking was influenced by factors related to knowledge and experiences, policy initiatives, and the social contexts in which they worked. This investigation reveals the complex nature of intervention implementation in schools.