A major new study, involving 5,000 youngsters aged 16-17 who left school in 2003, will make depressing reading for ministers who have put policies on inclusion and "closing the opportunity gap" at the heart of their agenda.
One striking figure from the Scottish School Leavers' Survey, the first since 1999, is that 71 per cent of those with a parent in a higher professional or managerial occupation achieved five or more Standard grades 1-2, compared to just 17 per cent of pupils from families in "routine" occupations.
And, while only 6 per cent of leavers in the highest social class failed to achieve any Standard grade 1-2 passes, this soared to 48 per cent for the lowest groups.
Parents' social class also affected subject results, with 77 per cent from professional families gaining a Standard grade 1 or 2 in english, against 32 per cent for those in the bottom social group; the respective figures for maths were 67 per cent and 15 per cent.
Family circumstances make a great difference to Standard grade results, the researchers concluded, representing an even bigger impact than gender divisions, "Although females continue to outperform males, when we consider the extent of these differences compared to the results according to social background, the size of the latter represents a considerably greater source of inequality," their report states.
"The analysis highlights the stubborn persistence of social class inequality in attainment, and in particular the cumulative advantage among the higher social classes who, despite rising overall levels of attainment, appear able to maintain their competitive advantage over other groups."
The lottery of birth also plays a part in staying-on rates: 88 per cent of those in the study who had a parent in a higher professional or managerial occupation stayed on at school after 16, compared with just 48 per cent of those with parents in routine occupations.
In turn, this widened the educational gulf between the classes. "Young people who left school before S5 or were Christmas leavers were more likely than later leavers to have truanted regularly, been suspended or expelled, or have no Standard grade at levels 1-2," the researchers report. "They were also more likely to have parents in the lowest social class."
Such experiences then led to differing aspirations, according to the survey. Asked what they would like to do in the future, 83 per cent of those from professional families said they wanted to go to university, compared with only 41 per cent of those whose parents were in routine jobs.
The latter group had a stronger interest in having a full-time job - 92 per cent against 88 per cent for the former.
Parents' education continues to be a key factor in the attainment of their children, which also reflects social background. This is particularly so where one or both parents have a degree: 60 per cent from such families achieved five-plus Standard grades 1-2 last year, compared to 30 per cent where neither parent had Highers.
Families made an additional contribution - 43 per cent who lived with both natural parents gained the top Standard grade results, compared with 25 per cent from single-parent households.
Even housing has an effect on results - 46 per cent of youngsters from privately-owned homes scored five or more Standard grades 1-2, well ahead of the 15 per cent who did so and lived in rented accommodation.