This article describes part of a larger action research study carried out in 2018 with secondary school learners and teachers of English in southern Argentina. The study was guided by two aims: (1) improving English language learner motivation, and (2) transforming the English as a foreign language (EFL) curriculum through teacher and learner engagement. The project also sought to help teachers develop professionally and exercise they agency as curriculum makers and developers through the support of teacher research. The study involved the participation of 920 learners in the design and implementation of EFL lessons which responded to their beliefs, expectations, and experiences. Data were collected through a survey, group and individual interviews, reflective journals, and whole class discussions. Drawing on thematic analysis and descriptive statistics, findings also show that learners moved from demotivation to motivation as they noted that they could contribute to curriculum enactment and transformation through active participation in teachers' pedagogical decisions. Findings also reveal that the enactment of a context-responsive and bottom-up curriculum led to motivational synergy, and teachers' agency enhancement through collaborative lesson planning, materials development, and research engagement for professional development. However, teachers experienced lack of confidence regarding teacher-made materials.