This paper reports on the development and validation of the classroom assessment (CA) for self-regulated learning (SRL) Questionnaire (CASRLQ), a questionnaire intended to measure to what extent CA practices are SRL supportive. The original CASRLQ, consisting of 32 items to represent five SRL-supportive CA dimensions, was constructed and administered to a sample of 469 Grade 11 students. However, the preconceived structure was not supported. We then used the same dataset (split into two) to explore and verify a new factor structure employing exploratory and confirmatory factor analyses. The questionnaire was then revised. A new sample of 630 Grade 11 students were surveyed to confirm the structure of the revised questionnaire. The final form of the CASRLQ consisted of 28 items and addressed seven CA features: assessment tasks, student choice, self-assessment, peer-assessment, instruction, teacher feedback, and CA environment. The CASRLQ proved to be a reasonably reliable and valid instrument suitable for use in quantitative investigations on CA-SRL-related topics. It could also offer some guidance for teachers' CA practice.