A common feature of very large undergraduate science units (e.g. biology, chemistry) is promulgation of teaching and assessment practices to ‘middle of the distribution’, which ignores the distribution extremes. Although there is a wide range of strategies that support poorly performing students in these units, very little work has been reported on catering for more capable or high achieving students, who may feel frustrated and poorly challenged in such settings. My research focussed on the development, introduction and evaluation of alternative assessment tasks into two first year science units, with the aim of providing more challenging learning opportunities for high performing students. Although neither special credit nor extra marks were associated with these tasks, eligible students appreciated the opportunity to undertake a more challenging assessment task, and strongly engaged with it, primarily due to the greater intellectual stimulation involved. Further, students who undertook an alternative assessment commented on the learning of new skills, and the sense of fun engendered by the chemistry group assignments. The outcomes of this initiative provide a foundation for further investigations of differentiated assessment models in undergraduate science.