The focus of this Q methodological study was to explore how professionals in the Educational Psychological Service (EPS) and schools experienced a system-based approach to expert assessment work. Forty informants from the EPS and schools sorted 60 statements about the assessment process. The following two shared viewpoints were identified: (1) teacher-focused EPS advisers and (2) principal-focused EPS advisers. While the two groups of EPS advisers seem to approach the school via either the teacher or the principal, joint collaboration on developing knowledge during the assessment process seems scarce in both viewpoints. The students' experience with school life is the least emphasized. Challenges related to collaboration on developing expert knowledge between the EPS and the student, teacher and principal are discussed. Three practical implications for the realization of a system-based approach to expert assessment work are suggested and further linked to implications for understanding and interpreting EPS's statutory task.