Objective: Psychologists have a responsibility to conduct standardised assessment according to instructions in test manuals and guidelines in assessment texts. In practice, circumstances arise that are not addressed in manuals and texts. The aim of this study was to explore the ways in which experienced psychologists manage some of these issues. Method: The participants were 10 psychologists with postgraduate training in assessment and reputations as experts within the professional community. Years of experience ranged from 5 to more than 30 years. Most of the participants had specialist area of practice endorsement in educational and developmental psychology. Participants responded to survey questions about aspects of assessment for which ready answers could not be identified in test manuals or published texts. Each participant was asked to explain and justify their decisions. Results: On some issues, participants tended to follow the way they had been taught. Other decisions were based on clinical experience, rather than on shared understandings or evidence from research. Conclusions: The findings highlight the lack of empirical research about best practice in assessment, the importance of ongoing professional development, and the need for rigorous training that addresses the many issues that arise in assessment and encourages ongoing reflective practice.