The proportion of children from deprived backgrounds is four times higher in secondary schools than in the grammar sector, according to figures based on the take-up of free school meals - the official poverty index used to allocate money to counter social deprivation.
Statistics for 199596 show that Protestant voluntary grammar schools have the fewest deprived pupils with only 2.9 per cent on free meals. By contrast, in controlled (Protestant) secondaries 26 per cent of pupils are eligible while Catholic secondaries take the greatest number of deprived children with 45.1 per cent on free meals.
These figures, combined with the latest exam results, show that children from manual backgrounds continue to lose out. Last year, 91 per cent of grammar pupils gained five or more good GCSE grades. The secondary figure was 27 per cent.
The statistics also show that nearly seven times more Protestant secondary pupils (25.9 per cent) than grammar pupils were eligible for free meals. On the Catholic side, the figures were 16.5 per cent for grammar and 45.1 per cent for secondary schools.
And one education and library board officer said: "I used to joke that entitlement to free school meals could be used to select children for secondary and grammar schools instead of the 11-plus. Now it is almost true."
The suggestion that Protestant working-class children are less likely to go to grammar school than their Catholic peers is supported by research on entrants to higher education in 1991 by Ulster academics Bob Cormack, Tony Gallagher and Bob Osborne.
They found that, despite improvements in the past 20 years, children from manual backgrounds were still seriously under-represented among university entrants - particularly Protestants, where the ratio of "manual" to "non-manual" students was 27:73, far worse than the Catholic ratio of 43:57.
Ken Reid, the Secondary Heads' Association's field officer and a former grammar headmaster, said: "In the nature of the Northern Ireland system people in a higher social class are always going to have an advantage because they can afford to give more support to their children and are probably more insistent on success in primary school and in the 11-plus.
"People in deprived areas, instead of seeing education as a way out, are so beaten by their deprivation that they send their children to the local school without question. Catholics have become more aware of the need for education, but Protestants have been slow to do anything about it."
But he warned that simply abolishing selection and sending children to neighbourhood schools would achieve nothing. "Higher expectations are very important. If your expectations are low you will get low performance, and probably poor behaviour as well."
The Northern Ireland Council for Educational Research reported in 1988 that middle-class pupils were much more likely to pass the 11-plus (46 per cent) than working-class candidates (22 per cent). Middle-class parents were also more likely to get their children into grammar schools than working-class parents whose children had the same grades.