The project described in this digest was designed with the belief that teacher professional growth can best be fostered through sustained collaborative inquiry between teachers and researchers. It set out to incorporate what is known about quality professional development with the special features necessary for meeting the needs of English language learners. The project defined a model of sheltered instruction based on the research of best practices, as well as on the experiences of the participating teachers and researchers. They collaborated in developing the observation tool being utilized in the study, the Sheltered Instruction Observation Protocol (SIOP), which identifies the features of sheltered instruction that can enhance and expand teachers' instructional practice. The SIOP was originally designed as an observation and rating tool for the researchers to use while viewing the participating teachers in the classroom. During the course of the project, however, the participating teachers discovered its potential as a tool for lesson planning and reflection. The model has been used to train middle school teachers to implement effective sheltered strategies in their classes in four large urban school districts (two on the East Coast and two on the West Coast). (VWL)