There is a significant need for new professional development options designed for mainstream teachers of English Language Learners (ELLs). This Phase I project will address the growing national need by defining an online Professional Development Resource (PDR) designed specifically for these teachers. The PDR will provide core concepts and strategies related to ELL instruction; it will be self-contained, easily accessed and navigated, and designed for use on an ongoing, as-needed basis, i.e., embedded in daily instruction. The PDR offers a new resource to fill a gap in viable options for mainstream teachers of ELLs. The PDR is expected to be particularly useful in settings where teachers work in dispersed locations, apart from other ELL teachers and resources. In Phase I Development Associates and its technology partners will (1) define the specifications for an initial PDR prototype; (2) review the design with user focus groups and Advisory Group experts; (3) build an initial (¿proof-of-concept¿) prototype; and (4) work with three partner school districts to pilot test the initial prototype. The Phase I products will be the initial prototype and a Functional Requirements Document, the blueprint for Phase II development and testing of a full online PDR prototype.