Maryland's Howard County, southwest of Baltimore County, has recently experienced unprecedented growth. Cultural and ethnic diversity have increased, as have poverty levels. Achievement gaps have appeared, budgets have been reduced and many experienced history teachers have retired, leaving a teaching force that needs the support of strong professional development. This 3-year graduate-level program will offer a 1-day fall colloquium, three Saturday sessions during the school year and a week-long summer institute. Participating teachers will represent all school levels, and priority will be given to teachers who lack history certification or those who teach at schools in need of improvement, and schools with heavy populations of underperforming students and English language learners. Historians and history education specialists will offer instruction on content and research-based teaching strategies. History Labs: Inquiry-Based Teaching and Assessments of American History in Howard County Public Schools will have participants read primary sources for content and understanding, carry out critical analysis, write evidence-based statements and interpretations, and engage in informed discussion of key historical questions and issues. The major classroom strategy will be inquiry-based instruction, and teachers will learn to create multiday history labs in their own classrooms. They will also develop formative and summative assessments to measure student progress. Each teacher ill implement at least five history labs, giving them experience they can use as master teachers to support colleagues after the grant period ends. The best teacher-created products will be available online as resources for other history teachers. The project will also create the "Assessment Resource Center for History," an online collection of formative and summative assessments categorized by time period and linked to national U.S. history standards.