Considering the broader context of school reform that is seeking education strategies that might deliver substantial impact, this article examines four questions related to the policy and practice of expanding learning time: (a) Why do educators find the standard American school calendar insufficient to meet students' educational needs, especially those of disadvantaged students? (b) How do educators implement a longer day and/or year, addressing concerns about both educational quality and costs? (c) What does research report about outcomes of expanding time in schools? and (d) What are the future prospects for increasing the number of expanded-time schools? The paper examines these questions by considering research, policy, and practice at the national level and, throughout, by drawing upon additional evidence from Massachusetts, one of the leading states in the expanded-time movement. In considering the latter two questions, the article explores the knowns and unknowns related to expanded learning time and offers suggestions for further research.