Employing students to market higher education (HE) and widen access is established practice in the United Kingdom and other developed countries. In the United Kingdom, student ambassadors are held to be effective in aspiration and attainment-raising work and cited as "role-models" for pupils. The focus of this paper is student ambassador outreach work in STEM (science, technology, engineering and mathematics including medicine) at two contrasting universities. The study deployed ethnography and approaches from across the social sciences to trace and analyse discourses surrounding ambassadors, and to explore their positioning within learning contexts, relationships with pupils and the learning that takes place. Findings indicate that where ambassadors work collaboratively with pupils in contexts with "informal attributes", pupils can identify closely with them. However, in contexts with more "formal attributes", differences, not similarities, are highlighted. Stakeholder interests are found to significantly impact on learning contexts and on ambassadors' efficacy as HE "role-models".