Many schools, districts, and states are looking for alternatives to the traditional seat time- and credit hour-based system. While mastery- or competency-based education (CBE) principles have a history in vocational settings, CBE models are new to the K-12 setting. The Proficiency-Based Pathways Project, funded by the Nellie Mae Education Foundation in partnership with the Bill and Melinda Gates Foundation, awarded grants to seven projects operating in 11 schools that employ a range of competency-based education models. The small public high schools are spread throughout urban, suburban, and rural New England and enroll fewer than 600 students each. This study documents each school’s experience, highlighting key components, benefits, and challenges. All programs in this study exhibited a measureable definition of mastery and a flexible use of time. Benefits found include higher motivation and engagement especially among struggling students, and challenges include inflexible state and district policies built around the credit hour and little guidance for curriculum design and lack of high-quality data to assess and monitor student progress.