There is great enthusiasm for curricula that place students and residents in community-based primary care practices and in rural and underserved areas. Interest in these primary care training experiences is based, in part, on studies that report that they can prompt learners to pursue careers in primary care specialties and underserved areas. Given that these programs attract learners with prior career interests in primary care and underserved area medicine, however, it might be that the favored career choices of their graduates are better explained by programs' selection than by their curricula. In studies where learners are randomly assigned to various training programs, no curriculum effect is found, at least for the typical one- or two-month primary care and rural rotation. Only in studies of longitudinal, multidimensional programs have career effects been demonstrated when learners are randomized. The need for a balanced physician workforce, and therefore the need for curricula to create it, demands ongoing, rigorous assessments of the efficacies of the various primary care training programs. Critical reevaluation will probably show that most schools and residencies need extensive curriculum changes if learners' careers are to be affected, and that admission committees can play a pivotal role in creating a balanced physician workforce. These discussions challenge educators to be as thoughtful and as empirically grounded as possible when changing the content and process of medical training.