Exploiting the potential that Assessment for Learning (AfL) offers to optimise student learning is contingent on both teachers' knowledge and use of AfL and the fidelity with which this translates into their daily classroom practices. Quantitative data derived from the use of an Assessment for Learning Audit Instrument (AfLAI) with a large sample (n = 594) across 42 primary schools in the Republic of Ireland serve to deprivatise teachers' knowledge and use of AfL and the extent to which AfL is embedded in their work. The data confirm that there is urgent need for high-quality teacher professional development to build teacher assessment literacy. However, fiscal constraints coupled with the fractured nature of current provision renders it impossible to offer sustained support on a national scale in the immediate term. In response, this paper proposes the adoption of a design-based implementation research approach to site-based collaborations between researchers, teachers and other constituent groups, such as that engaged in by the authors over recent years, as a mechanism for addressing teachers' needs in a manner that also supports other participants' professional interests.