In Australia, concerns about the quality of mathematics education that students experience are particularly salient in rural schools. These schools typically report great difficulty in attracting and retaining qualified teachers of mathematics. Teachers in non-metropolitan locations may also experience professional isolation if they have limited access to professional development opportunities. This article reports on a year-long research and development project that provided such opportunities to teachers in ten rural and metropolitan schools in South Australia. Its purpose was to help the teachers plan and implement numeracy strategies across the school curriculum. The project was informed by a new model of numeracy whose elements comprise mathematical knowledge, dispositions, tools, contexts, and a critical orientation to the use of mathematics. To investigate the effectiveness of the numeracy model and the professional development approach, data were collected via lesson observations, teacher and student interviews, and written tasks that tracked changes over time in teachers' understanding of numeracy. Most teachers began the project with a concern for improving students' mathematical knowledge or dispositions, but then gradually incorporated other elements of the model into their planning and practice. A case study of an early career teacher in a rural school illustrates one developmental trajectory through the elements of the model. Teachers identified time, openness, collegiality, and accountability as features of the professional development approach that contributed to its effectiveness. Implications for sustainability and scaling up are discussed, especially with reference to supporting teachers in rural schools.