The fourth year of medical school has been repeatedly found to be ineffective, and concerns exist about its purpose and academic quality, as well as grade inflation. Since Flexner, the purpose of undergraduate medical training has moved from readiness for independent practice to readiness for postgraduate training. However, training directors report that medical graduates are inadequately prepared to enter residency. The authors propose a fourth year with two components: first, a yearlong, longitudinal ambulatory experience of at least three days each week on an interprofessional team with consistent faculty supervision and mentoring, increasing independence, and a focus on education; and second, rigorous clinical-scales-based assessment of meaningful outcomes.In the proposed model, the medical student has generous time with a limited panel of patients, and increasing autonomy, with faculty moving from supervising physicians to collaborating physicians. There is regular assessment and formative feedback. This more independent, longitudinal clinical experience uniquely allows assessment of the most meaningful work-based performance outcomes-that is, patient outcomes assessed by validated clinical scales. The proposed fourth year will require a realignment of resources and faculty time; however, models already exist. Barriers and possible solutions are discussed.A purpose-driven, assessment-rich fourth year with patient and supervisor continuity will provide real-world experience, making medical graduates more competent and confident on the first day of residency. Use of clinical scales will also allow educators new confidence that the performance-based competence of these more experienced and expert graduates leads to demonstrable collaboration, healing, and good patient outcomes.