This documentary account describes professional development for teachers in the USA serving culturally and linguistically diverse students. The purpose of the project was to monitor effectiveness of training in Sheltered Instruction Observation Protocol (SIOP) and to assess the value of cognitive coaching. Quantitative and qualitative data sources were employed, including a knowledge test, surveys, and interviews. Findings indicated workshops were effective and produced strong commitment to the model, but resulted in a disappointing level of implementation without a coaching phase. Results illustrate the criticality of time allocation for cognitive coaching, and teachers articulate specific changes they made in their instruction. (Contains 3 tables.)