Teacher evaluation and teachers' professional learning are too often confined to separate areas of research and professional practice. Rather than approach evaluation and enquiry as distinct or irreconcilable, this paper applies the ideas of Stenhouse to explore new possibilities for the reappropriation of mandated appraisal in ways that support teachers' professional growth. Illustrative case studies of laboratory schools in the United States and England are used to examine the interaction of local and lateral forms of professional accountability with external and hierarchical regulatory frameworks. The article reports the design and enactment of change in two schools (a US kindergarten through twelfth grade school and a UK high school) connected through the International Association of Laboratory Schools (IALS) that purposively redesigned appraisal over a three-year period to build capacity for collaborative curriculum enquiry. Attention is afforded to the space for manoeuvre between advisory and mandatory guidance, and the challenges to relational trust and collective responsibility posed by performance-based accountability systems. The findings provide new insights into how teacher-led collaborative enquiry (curricular co-design) can address the unintended consequences of test-based accountability and rubrics-based observation as principal drivers of educational improvement.