traditionally, the assessment of student learning in medical education has relied almost entirely on written exams. but there would seem to be more to being a competent practitioner than could ever be assessed using a paper and pencil test. barrows' pioneering work on training actors to serve as simulated patients opened the door to a new way of evaluating clinical skills. simulated patients could be used to test the students' interactional and problem-solving skills. this kind of "performance-based" assessment has now been incorporated into national licensure exams for all u.s. medical students.