A new "controlled assessment" model was introduced in England, Wales and Northern Ireland in 2009. This paper describes a research project that explores teachers' experiences of this new assessment model in General Certificate of Secondary Education (GCSE) level modern foreign language (MFL) speaking assessment. Focusing on teachers' school-based assessment roles, task design practices, marking and grading perceptions, and support and feedback needs, the paper frames discussion around the validity of the assessment process. Using a socio-cognitive framework, which breaks validity into contextual, cognitive and scoring components, the paper analyses teachers' experience to gain insight into the areas of assessment knowledge that misalign with the awarding organization developing the assessment. The use of the socio-cognitive framework also presents an opportunity to identify where potential threats to validity exist within the assessment system, and the study considers the interactions that should take place between teachers and assessment developers to mitigate misaligned intentions and enacted practices in assessment model design.