Research and development on formative assessment has paid little attention to part-time adult basic education in informal community-based settings. A three-year project funded by the Nuffield Foundation, the National Research Development Centre for Adult Literacy and Numeracy, and the Quality Improvement Agency addresses that gap in vocational and adult basic education. It explored factors that help and hinder change to teachers' formative assessment practices, and the ways in which different "learning cultures" affect different approaches to formative assessment. The project used a problem-based approach to professional development that rejects simple, top-down "recipes" and guidance for "best practice". This paper evaluates critically the effects of the "learning culture" on whether teachers' formative assessment practices were in the "spirit" or "letter" of assessment for learning in adult literacy and numeracy classes, drawing on interview and observation data from six classes in two very different organisations. (Contains 2 tables.)