A study by the party of the 2001 post-appeal exam results shows a significant 7 per cent gap in performance at three or more Highers between faith and non-faith schools with a free school meal entitlement (FSM) of 22.83 per cent, the average in Catholic schools.
Brian Monteith, the party's education spokesman, said: "Whichever way we looked at it, Catholic schools are clearly punching above their weight."
Tory researchers examined 39 non-denominational secondary schools with similar characteristics to their Catholic counterparts. The average number of students passing three Highers or more in S5 is lower in Catholic schools but they have a higher than average number of pupils on free meals.
The Tories applied "regression theory" to the statistics to show that they might be expected to have a pass rate of 18.8 per cent, not the 21.5 per cent they achieve.
Mr Monteith accepts criticism that free meals entitlement is a crude indicator but maintains it is a fair use of the figures. "Crucially, Catholic schools are having the biggest impact where it is needed most, helping those living in poverty and with low expectations," he said.
The Tories are using their evidence to support expansion of faith schools, which appear to produce a better learning culture.
Lindsay Paterson of Edinburgh University, an acknowledged expert on Catholic performance, said the figures confirmed evidence from surveys dating back 40 years, although he would challenge the use of averages and free meals.
His own findings, based on the 1994 leavers survey, showed a 2-3 per cent advantage for working-class Catholic students. For middle-class students, this was reversed with a 1 per cent gap in favour of non-denominational schools.
Even more significantly, 65 per cent of working-class Catholic students who gained three or more Highers went on to higher education against 56 per cent of similar students in the non-faith sector.
Studies in France and the United States have shown similar evidence of working-class students doing better in Catholic schools. This is attributed to the "cultural capital" of belonging to a faith community, what schools now term as ethos. Professor Paterson also believes Catholic schools are more comprehensive in their intake.
John Oates, field officer for the Catholic Education Commission, said the findings confirmed that faith schools were good for the Catholic community and for Scotland. "But I think that this requires further research and I would hope the Scottish Executive would consider that," Mr Oates said.
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