We present principles for the design of an online system to support computer algebra enabled questions for use within the teaching and learning of mathematics in higher education. The introduction of a computer algebra system (CAS) into a computer aided assessment (CAA) system affords sophisticated response processing of student provided answers. Randomised question parameters and immediate, tailored feedback support a pedagogy of practice. We introduce a mathematical question type that encapsulates these features and describe its implementation within the CABLE online system. In CABLE, the question authoring process is supported through options and by providing a programming-free interface for teachers. (Contains 6 figures and 1 table.)