We describe and evaluate an approach to student learning that aims to instil a culture of formative assessment based on peer-assisted self learning, instead of a marks-based culture in which learning effort is rewarded with marks that contribute to the student's degree. The idea is for suitably qualified third- and fourth-year undergraduates to assist in the running of weekly first-year tutorials. They mark submitted work, provide written and verbal feedback on the students' performance and lead problem solving discussions during tutorials. However, contrary to normal practice, the marks they award do not contribute to the students' year total; all tutorial work becomes essentially voluntary. We report results from a pilot implementation of the scheme over a 12-month period in an engineering department at a leading academic institution. The set-up of the scheme was such that a comparative and triangulated assessment was possible amongst the students and tutor team. There was no\r\ndiscernible degradation in student attendance, submission rates and performance in either the weekly exercises or end of year examinations. Further analysis demonstrates that this type of peer-assisted learning improves some key aspects of student learning, and provides important benefits to the senior peers in terms of their own personal development. We conclude that the scheme provides an excellent alternative to traditional learning methods whilst substantially reducing the investment in academic staff time.\r\n