Catholic secondaries are outperforming other schools despite wrestling with profound changes to their student and teacher populations, according to an analysis by the former chief executive of the General Teaching Council for Scotland (GTCS).

Anthony Finn, also professor in education at the University of Glasgow, said the days had “probably gone” when such schools were exclusively Catholic concerns, but their emphasis on values had been credited with keeping educational standards high.

Professor Finn found that 30 per cent of inspection outcomes in non-denominational secondary schools over two years were rated “excellent” or “very good” by inspectors, compared with 51 per cent for Catholic secondaries. And while 36 per cent of outcomes in non-denominational schools were “weak” or “unsatisfactory”, in Catholic schools the figure was 13 per cent.

Each school is rated on five standard outcome categories. Professor Finn examined 99 inspection reports for state secondaries “of a meaningful size” from the period between February 2012 and last month, including 14 for Catholic schools.

He revealed his findings when delivering the annual Cardinal Winning Education Lecture in Glasgow this month. Professor Finn, who left the GTCS last year and chairs the Scottish College for Educational Leadership, said he did not claim his analysis was statistically valid but argued the results were “interesting”.

Although most schools in Scotland were “performing quite well”, the overall performance of Catholic schools in the sample was “even better”, he said. “Not only are Catholic schools regularly judged to be caring, inclusive establishments in which positive values are nurtured, they clearly also offer high-quality education and deliver good results,” he added.

Professor Finn, headteacher at Catholic comprehensive St Andrew’s High in Kirkcaldy for 17 years, also explored how education in Scotland had changed over the decades. “In the past, we openly depended on practising Catholic teachers teaching Catholic children in Catholic schools,” he said. “We should now accept that these days have probably gone.”

Although some schools reported more than 90 per cent of students as being Catholic, others told Professor Finn that their proportion of practising students might be as low as 30 per cent. Some schools had high proportions of Catholic attendees but relatively few teachers within the faith - as low as a third in one secondary.

Professor Finn praised the commitment of non-Catholic teachers in most Catholic schools but said institutions could not depend on that level of commitment from those who were not of the faith. They needed a strong complement of reliable Catholic teachers, he argued.

School leaders were also faced with difficult choices over staffing, he said, along with concerns about inconsistency in how priests granted approval for teachers. “If you had to choose between a very good teacher who is not Catholic and what we might best describe as an adequate Catholic teacher, which would you choose?” he asked. “And if you already have in your school a good teacher who is committed to the school but may not be eligible for approval, would you not, like some heads, become frustrated?”

Professor Finn also highlighted a recent Scottish government report which found no evidence that Catholic schools helped to promote sectarianism. “Catholic schools are not narrow or inward-looking; they provide a positive service to very wide communities. They never did and never could support such an evil prejudice,” he said.

Michael McGrath, director of the Scottish Catholic Education Service, said that successful Catholic schools shared traits including a vision that was focused not only on educational objectives but on a way of life and “a commitment to justice for all and a preference for the most disadvantaged”.

The general secretary of School Leaders Scotland, Ken Cunningham, said that any school, Catholic or otherwise, should be praised if it emphasised “the importance of values, trust and community”.

Education Scotland preferred not to comment on Professor Finn’s lecture, pointing instead to its recent report on religious education, in which Catholic schools were praised for making the subject central to school life.