On the face of it, the top-performing secondary school in Wales is a voluntary-aided Catholic day and boarding school in Denbigh.

Ninety per cent of St Brigid’s all-female GCSE students clocked up five or more passes at grades A*-C last summer.

But statistics released this week by the Assembly government suggest the laurels should also go to a handful of inner-city schools with pass rates nearing the national average for Wales - despite a third or more of pupils being entitled to free school meals.

Sandfields comprehensive in Port Talbot is one of those deserving of praise, according to David Reynolds, professor of education at Plymouth university and a Welsh education commentator.

Almost a third of its 700 pupils are entitled to FSMs. But this year, 51 per cent of its Year 11 pupils passed five or more GCSEs at grades A*-C - close to the Welsh average of 52 per cent.

The achievement is even more notable when you discover the figures include children with moderate and severe learning difficulties attending the school’s special needs unit.

Professor Reynolds said: “The variation in performance between schools that have the same catchment area as judged by FSMs is fascinating.

“There are some outstanding success stories like Sandfields, and we can learn from schools that are doing well. You could find many schools in Wales with more advantaged pupil intakes (based on FSMs) with nowhere near the same results.”

Mike Gibbon, Sandfields headteacher, said the school had been working on target-setting and improvement strategies for the past five years.

It uses nferNelson’s cognitive abilities test (CAT) with Y7 pupils, and Durham university’s YELLIS (Y11 Information System) to assess children’s progress and help them focus on improving performance.

In association with its cluster primary schools, it is now using CATs with Y5 pupils in preparation for their arrival at Sandfields in two years’

time.

Mr Gibbon said: “It is formative data which will give us information about areas where a child needs extra attention. You have to make it pupil-centred.”

But he is cautious about publishing raw data on results.

“There is a long way to go in educating people who pick up the newspaper and just look at the raw statistics. There is a lot more in terms of value-added and contextual information that needs to be reflected in the statistics.”

That concern is echoed by the teaching unions. Geraint Davies, secretary of the NASUWT Cymru, said: “There are so many factors that influence a child’s education, not just FSMs. You need to look at special needs, parental backgrounds and levels of attainment,” he said.

“The reasons why some schools are underperforming will be pertinent to that particular school.”

The pass rate for five A*-C grade GCSEs or equivalent in Wales’s 230-odd secondary schools ranges from 14 to 90 per cent, with FSMs from 2.3 to 64 per cent.

Top 10 schools in Wales

Schools ranked by five A*-C grade passes (FSMs in brackets):

1 St Brigid’s, Denbigh - 90 (7) 2 Ysgol Gyfun Bro Myrddin, Carmarthen - 87 (2.3) 3 Bishop of Llandaff CIW high school, Cardiff - 86 (4.5) 4 Cowbridge school, Vale of Glamorgan - 85 (2.6) 5 Bishopston comprehensive, Swansea - 82 (5.3) 6 Eirias high school, Colwyn Bay - 81 (14.2) 7 Ysgol Dinas Bran, Llangollen - 81 (11.3) 8 Cardiff high, Cardiff - 80 (3.5) 9 Stanwell comprehensive, Penarth - 79 (6.5) 10 Caerleon comprehensive, Newport - 79 (3.1)