Parents of students who study abroad on Erasmus programmes tend to be more highly qualified than the parents of other students, according to a European Commission report.
The report aimed to investigate whether students who took the opportunity to spend time in another country came from different social or economic backgrounds from other students.
It found little evidence that Erasmus students were better off than most, except in countries where students tended to live with their parents and had little direct national student support.
Nor were the parents of Erasmus students in particularly well-paid or high-status jobs, compared with those of other higher education students.
But family educational background did appear to make a difference.
While about 30 per cent of heads of households that include students hold a higher education qualification, the figure rises to 59 per cent for Erasmus students.
The report states: "It might be assumed that the most highly qualified parents are more conscious of the need for education in foreign languages and other cultures in order to provide opportunities for their children to develop initiative and independence... It could also be that knowledge of the exchange programme is more widespread in these families."
The fact that bias appears to be based on cultural rather than economic grounds makes it especially difficult to combat, says the report.
It suggests that student organisations acting at a European level could help through information campaigns targeted at poorly represented groups.
The report, which surveyed more than 20,000 students - nearly a quarter of those who took part in the 1997-98 Erasmus programme - had an overall response rate of 46 per cent.
It identified problems in the take-up rate for the programme - since confirmed by more recent figures - of only half the number of places available taken up in 1997-98.
The United Kingdom had the lowest take-up rate, except for Greece, at 39 per cent. But it
had the highest take-up of places from incoming students at 65 per cent.
While more than 90 per cent of all Erasmus students said they were happy, academically, with their experience of the programme, British students were among the most dissatisfied, with 14 per cent reporting a negative academic impression of their time abroad.