Since 2000, and especially during the United Nations Decade of Education for Sustainable Development (DESD 2005-2014), many universities have begun offering educational programmes on sustainability. Over this span, the level and type of diversity among students have only increased. This begs the question: How does university student diversity affect sustainability education? What is productive and confounding about learners' cultural and academic heterogeneity? This research draws on a literature review, a survey of university students studying sustainability in Japan and an observational study. The results demonstrate that interaction between students from different cultures and disciplines clearly improves skills for sustainability education, especially critical thinking and problem solving. Moreover, the surveyed students expressed interest in and appreciation of opportunities to expose their sustainability research themes to audiences of various research fields.