In contrast to theoretical and empirical insights from research into formative assessment in compulsory schooling, understanding the relationship between formative assessment, motivation and learning in vocational education has been a topic neglected by researchers. The Improving Formative Assessment project (IFA) addresses this gap, using a sociocultural approach to explore the relationship between formative assessment practices and "learning cultures" in vocational education. This article explores the influence of learning cultures in vocational education on the practice of formative assessment and evaluates critically two closely related questions. Why do some learning cultures foster formative assessment that leads to instrumental learning while others develop deeper forms of learning? When is formative assessment a springboard for sustainable learning, and when does it remain an instrumental straitjacket? (Contains 1 note.)