The proportion of Scots from the 20% least advantaged backgrounds going to university increased by just one percentage point – from 10.6% to 11.6% – between 2005/06 and 2010/11.
NUS Scotland, the student body that produced the report, said it would be at least 2050 before 20% of the university population was from the benchmark area.
In response, the students' organisation has called for a controversial shake-up of admissions procedures to allow universities to consider students from poorer backgrounds who have lower grades than the normal benchmarks.
The findings follow revelations in The Herald that some universities had been recruiting tiny numbers of poorer students, with St Andrews, where Prince William studied, recruiting only 13 students from the most deprived backgrounds in Scotland in 2010/11.
Robin Parker, NUS Scotland president, called on the Scottish Government to press ahead with proposals to give universities binding targets on access backed up by legislation, with the threat of financial penalties for those that fail.
Mr Parker said: "Achieving fair access is not about some kind of social engineering or charity. It's about getting the best people into our precious university places.
"If universities fail on widening access they're failing on their most central of missions – getting the most talented people into university."
However, Alastair Sim, director of Universities Scotland, which represents university principals, said the matter was the responsibility of all education sectors.
"Further progress at university level is inextricably linked to addressing the ways in which deprivation can limit learners' opportunities, from nursery level all the way up to Highers and beyond," he said.
The report, Unlocking Scotland's Potential, found that, for every pupil recruited by universities from the 20% most deprived communities (according to the Scottish Index of Multiple Deprivation), 2.5 are admitted from more privileged backgrounds, but the ratio rises to one in 16 for the most elite institutions – and to one in 28 for St Andrews.
It further identified large disparities in progression to higher education from different areas in Scotland.
The top two parliamentary constituencies in Scotland for progression are Eastwood, in East Renfrewshire, and Edinburgh Southern, with 68% and 52% of all school leavers going to higher education courses at either college or university.
The bottom two constituencies are Banffshire and Buchan Coast and Glasgow Provan, with 26% and 25% of all school leavers going on to higher education.
The report went on to highlight the introduction in England and Scotland of alternative admissions schemes which take account of the circumstances in which a pupil was educated and not just their exam results.
They show students from more deprived backgrounds accepted with lower grades, or those who had their grades "topped up" after attending summer schools, can at least match, and often outperform, counterparts with higher grades from less deprived backgrounds.
"This should, once and for all, dispel the myth that school grades are the only, or even the best, way to judge an applicant's academic potential or ability to perform at university. Seen in this light, widening access is the pursuit of excellence not something that jeopardises it," the report states.
Other recommendations include talent spotting bright youngsters from an early age so they can be mentored. NUS Scotland also wants to see the setting up of an independent widening access unit.
Scottish Liberal Democrat leader Willie Rennie said last night: "Access to universities to those from poor backgrounds needs to improve. The SNP must work closely with the NUS and get a grip of university access."
Liz Smith, education spokeswoman for the Scottish Conservatives, added: "Our priority should be making every school in Scotland a good one, not setting entry targets for universities."
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