The underrepresentation of persons from socio-economically disadvantaged backgrounds in higher education in countries such as Australia is of policy concern. In order to be able to identify such individuals for targeted interventions and to monitor their participation rates, it is necessary to have an accurate, simple to administer, and relatively inexpensive method of measuring students' socio-economic characteristics. We demonstrate that the postcode methodology currently used by the Australian Department of Education, Training and Youth Affairs (DETYA) for monitoring purposes, while being relatively simple and inexpensive to administer, is subject to considerable error. A student is allocated the `average' socio-economic status (SES) of all persons living within their residential postcode area, but areas can contain a mix of people from low, medium and high socio-economic backgrounds. In order to identify more accurately low SES students, we develop measures based upon the characteristics of individual students, rather than the characteristics of the area in which they reside. These new measures are based upon the results of the Participation in Higher Education Survey. This survey was conducted in the second half of 1997 and was based upon a sample of approximately 3000 first year students enrolled at a range of campuses throughout one Australian State. Our findings suggest that individual-based measures relating to the occupation and education of parents at the time when the student was in high school are appropriate for the classification of both recent school leavers and mature aged students. Together, these characteristics represent the family socio-economic situation while the student was attending secondary school.