Over the past 15 years, "assessment for learning" (AfL) has emerged as a key area of teacher practice with policy mandates around the world supporting teachers' implementation of the underlying components of this pedagogical approach. While procedural and selective implementation of AfL strategies has been observed within research (i.e., implementing the "letter" of AfL), promoting a "spirit" of AfL appears far more challenging. There is a critical need to better understand how teachers develop AfL capacity within their practice to effectively cultivate a spirit of AfL in their classrooms. The purpose of this study was to describe a learning continuum for teachers' implementation of AfL as based on data from 88 teachers. Specifically, interview and observational data were analyzed to describe five developmental stages demarcating shifts in teachers' conceptual understandings and enacted AfL practices. The resulting learning continuum provides an empirical foundation for responsive teacher education that facilitates teachers' continued learning toward more meaningful AfL implementation.