Objective Psychological assessment is a key activity for psychologists and a foundational element of psychology training, and psychological assessment supervision differs from psychotherapy supervision. The present study investigated factors that promote effectiveness in psychological assessment supervision. Method Participants were 47 assessment practica students at a clinical psychology doctoral program in the USA, their supervisors, and faculty evaluators of the Clinical Qualifying Exam‐Assessment (CQE‐A), which was the student competency outcome measure. Students were grouped by CQE‐A performance: pass (n = 15), remediate (n = 23), and fail (n = 9). Results Successful students performed better on tasks that required them to integrate complex client information, reported more supplemental supervision experiences, such as in group or provided by unlicensed advanced trainees, and indicated that supplemental experiences were associated with greater confidence. Successful students were rated as more able to manage anxiety during the CQE‐A and to use practicum supervision effectively. Students who failed reported greater focus in supervision on basic skills, and demonstrated inaccuracy in skills self‐assessment. Student satisfaction was positively correlated with regular monitoring, ongoing feedback, clear goals and expectations, clear evaluation criteria, an initial baseline skills assessment, regular meetings, and supervisors staying updated. Conclusions Linking skills assessment, goal setting, and evaluation are important for successful student outcomes. A developmental approach may aid in customizing supervision. Tools, such as supervision agreements and training to orient students to the process of assessment supervision, may impact student ability to use supervision effectively. Group and supplemental supervisors can aid in monitoring students and fine tuning skill development.