Becoming a physician or other health care professional is a complex and intensely developmental process occurring over a prolonged period of time. The learning path for each medical student, resident and fellow varies due to different individual learner abilities and curricular designs, clinical contexts, and assessments used by the training program. The slow and uneven evolution to outcomes-based medical education is partly the result of inadequate approaches to programmatic assessment that do not fully address all essential core competencies needed for practice or account for the developmental nature of training. Too many assessments in medical education still focus on single point-in-time performance or function as indirect proxies for actual performance in clinical care for patients and families.Milestones are a modest first step of providing predictive, longitudinal data on a national scale. Longitudinal Milestones data can facilitate the continuous improvement efforts of programs in assessment. However, Milestone judgments are only as good as the assessment data and group processes that inform them. Programmatic assessment should be longitudinally focused and provide all learners with comprehensive and actionable data to guide their professional development and support creation of meaningful individualized action plans. Efforts are urgently needed to rebalance programmatic assessment away from an overreliance on assessment proxies toward more effectively using developmentally focused work-based assessments, routinely incorporate clinical performance and patient experience data, and partner with learners through iterative co-produced assessment activities.