This paper aims to encourage teachers in higher education to reflect on the criteria they apply when assessing students' academic writing. Grounding its arguments in readings of postgraduate students' texts, the paper identifies complexities that evaded the teachers' assessments. These complexities are made visible by the development of particular theoretical perspectives. The concept of the "motivated sign" is given central significance in view of its relevance to the increasing diversity of student histories and expectations in higher education classrooms in the UK.