In a climate of growing accountability for Higher Education, there is an increased demand on assessment to play an evaluative role. National, professional and institutional quality assurance systems expect that the assessment of student performance can be used to evaluate the quality of teachers, learners, programmes and even institutions for the purposes of programme review, programme accreditation and institutional audits. While affirming the role of assessment as a catalyst for the improvement of teaching and learning, this paper problematises the use of assessment for evaluative purposes. Drawing on an Engineering Council of South Africa (ECSA) accreditation exercise, we illustrate the limitations of particular forms of assessment data as evidence of quality. The paper argues for assessment as a socially situated interpretive act and for validation as the on-going process of strengthening the alignment between our assessment tasks, procedures and outcomes, and the educational, political and social purposes which our assessment systems claim to serve. The central argument of the paper is that key source of assessment evidence for quality assurance purposes is to be found in the strength and effectiveness of programme validation systems.