The basic theory is that low SES applicants are disproportionately affected by movements in the number of places in the higher education system, so that when the number goes down they get a declining share of the total, and when it goes up they get an increasing share.
This is because low SES school students tend to get lower average Year 12 results, the currency for ‘buying’ admission to university. Other things being equal, a contraction in places causes admission requirements to rise and prices low SES applicants out, while an expansion causes admission requirements to fall and allows low SES students to buy more places.
The 2008 enrolment statistics released yesterday show that commencing domestic undergraduate numbers were up 1.5% on the previous year, allowing a modest increase in low SES* share from 16.95% to 17.01% (overall this series is very stable; most years rounding makes it flat).
Breaking the statistics down further, in the public universities 17.3% of commencing undergraduates are from low SES backgrounds, compared to 15.2% in non-public university providers- even though most of these students are paying full fees.
* This is using the postcode measure of low SES; permanent residence in a postcode in the lowest 25% according to the ABS Index of Education and Occupation.