Professional development for teachers is a complex and multifaceted endeavor and is becoming more so as popularity grows for standards-based education. Teachers generally report feeling pressure to cover the curriculum at nearly any cost. For English language learners, the cost is greater than usual as teachers often inadvertently ignore the language needs of these students in content courses. 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 has 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 has 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 (Echevarria, Vogt, & Short, in press). The protocol is composed of 30 items grouped into 3 sections: Preparation, Instruction, and Review/Evaluation. Items are further clustered under Instruction: Building Background, Comprehensible Input, Strategies, Interaction, Practice/Application, and Lesson Delivery. Items are scored using a Likert scale with scores ranging from 4 to 0.