In studies of language policy and planning (LPP) in schools, agency has often been understood in terms of how the impact of teachers, students and parents influence the implementation of top-down macro LPP or of the ways that community stakeholders generate LPP from below (Wiley & García, 2016). Such studies have emphasized the agency of various school community actors in shaping LPP in their local context (Alexander, 1992). This chapter will consider the question of agency from the perspective of the school as an ecological context in which actors claim agency in school-based LPP and explore the ways that the local ecology has an impact on, and constrains possibilities for, exercising agency. It will do this by examining the process of a school-initiated curriculum change to increase time for the study of foreign languages in a particular school as a case study of teachers’ agency in changing a school’s LPP. It will investigate the ecology of forces that influenced the exercise of the language teachers’ agency as language planners within the school and the ways that this ecology of forces constrained their agentive possibilities. It will consider in particular the impacts of prevailing ideologies of education and the place of language study within education, conceptualizations of curriculum as a cultural artifact, structural features of school organization, and professional relationships between teachers of different disciplines. As the language teachers worked to design and implement the new curriculum, these forces worked in different ways to constrain their possibilities for acting and ultimately led to the failure of the initiative.