Teaching medical students to spontaneously identify biopsychosocial issues (e.g. family violence) remains a challenge. We examined the extent to which using unannounced standardised patients (SPs) presenting in a clerk's clinical setting could assist with this teaching challenge. All clerks attended a family violence seminar in their family medicine rotation. Intervention students additionally saw an unannounced SP portraying 1 of 2 scenarios in their preceptor's office during the rotation, and received immediate feedback about their performance. An end of rotation objective structured clinical examination (OSCE) included an SP presentation similar to that seen by the intervention students. Clerks who received the intervention demonstrated increased questioning about family violence, from 0% (0 of 29 students) to 19% (5 of 26 students) in 1 OSCE scenario (P = 0.019), and from 40% (12 of 30 students) to 76% (19 of 25 students) in the other (P = 0.007). Seeing unannounced SPs had a dramatic effect on later student performance. This potentially powerful intervention could be applied to a range of clinical issues.