This article argues that differing disciplinary assessment cultures are likely to be an important factor in explaining differences in student marks and grades both within and between higher education institutions. Using institution-wide data on undergraduate student marks over the last five years in one UK higher education institution we demonstrate variability in the distribution of marks in terms of the 'distance travelled'. This issue was further explored via interviews with senior teaching-active staff. We suggest that the distribution of marks is likely to reflect different disciplinary assessment cultures as well as complexity in the process of marking and assessment. These findings signify that it will be highly challenging, if not impossible, to establish nationally comparable learning gain measures using student mark data because of the underlying inconsistencies in the process of awarding marks. In the current higher education context, with the ongoing implementation of the Teaching Excellence Framework, it remains important to debate and further investigate these issues with all stakeholders, including students.