Almost a quarter of Wales’ 22 councils have no schools in the top band of a system which identifies the best and worst performers.
Schools have been placed into one of five bands based on GCSE exam performance and pupil attendance.
In more than a third of areas, there are no schools in the bottom band.
The Welsh government denies the claims of teaching unions who say the rankings “name and shame” struggling schools.
Schools with the best scores are placed in Band 1, whereas those with the worst are in Band 5.
Merthyr Tydfil, Powys, Torfaen, Blaenau Gwent and Ceredigion have no schools in Band 1.
At the other end of the scale, there are no Band 5 schools in Neath Port Talbot, Newport, Pembrokeshire, Vale of Glamorgan, Torfaen, Carmarthenshire, Conwy, Denbighshire and Flintshire.
Education Minister Leighton Andrews said: “If we are to drive up standards across the board in Wales we need to know how our schools are performing. Banding is at the heart of this.
“It’s not about labelling, naming or shaming, or creating a crude league table. It is about putting schools into groups to identify which need our support and which we can learn from.
“You cannot un-invent the Freedom of Information Act – parents and pupils have a right to know what is best in Wales and how their schools measure up.”
Anna Brychan, director of the National Association of Head Teachers Cymru, said a single grade could not represent the entirety of what a school does.
“We are especially worried that the achievements of schools in lower bands, particularly those that are improving year-on-year by focusing tirelessly on standards and relying on their staff and communities to go the extra mile, will go unrecognised,” she said.
“This will damage the morale of the very people who are making a crucial difference to pupils’ lives.”
The banding system is being introduced as part of 20 reforms to drive up standards.
Plans to band primary schools are currently being developed, although it was revealed at least 30% would be exempt from the process because they had too few pupils to produce reliable data.
Dr Stevie Upton, a specialist in Welsh school performance, said parents who are concerned about the results of the banding should use the information as a starting point for a discussion with schools.
“Many of the measures that are within this particular banding system are indicators that have been used for a long time already, they are things that schools will recognise,” said Dr Upton.
“The issue of whether putting them together is helpful is another matter.
“But the simple fact is we have it now and we need to work out how to use it constructively.”
Teaching unions claim the new system is tantamount to a return to league tables and accused the government of introducing a “branding system”.
Branding by banding
David Evans, NUT Wales secretary, said teachers “strongly opposed” the process.
“This naming and shaming is something that we in Wales were proud to have moved away from, and it is a real shame that the government has decided to return to what is an outdated and restrictive practice,” he said.
The Association of School and College Leaders Cymru, which represents headteachers, was also critical.
“Branding by banding, via media headlines, will do little to raise standards for students given that the support available to schools, currently, merely consists of criticism and offers nothing in resolving the obstacles which are impeding progress,” its spokesperson, Gareth Jones, said.
Without know a school’s overall score, it is possible to use the date to tell how close to the boundaries of each band a school falls, nor exactly how much better or worse a school has performed over time.
According to the Welsh government, the system’s purpose is to identify schools in need of support, although extra funding will not be made available to schools in need of improvement.
Schools in the bottom bands will instead receive support from four new regional school improvement services, which will be run by groups of local authorities.
However, BBC Wales understands the support services will not be operational until September 2012.
Dr Philip Dixon, director of the Association of Teachers and Lecturers Cymru, said the promised support for schools in the lower bands was failing to materialise.
“Schools want to know what new and extra resources they will have to improve their performance,” he said.
“We are afraid that we could see the situation where schools labelled as underperforming are just left to languish without any effective support.
“The government needs to act quickly if it is to avoid creating a demoralised workforce.”
Analysis by Ciaran Jenkins, BBC Wales education correspondent
Schools are going to be placed in one of five bands whether they like it or not.
And all the indications are that they do not like it one bit.
It will now be clear to everyone which schools the Welsh government considers to be the worst performing in the country.
And what happens when those schools have been, as three teaching unions put it, “branded”?
Well, that’s when the extra support is supposed to kick in. The problem? These services won’t actually exist until September 2012 – too late to help schools improve before next year’s bands are published.
The Welsh Government says there will be extra support in the meantime.
So what’s the point? The answer is that the system is supposed to help schools to make progress.
However, because the overall scores of each school won’t be published, it will be impossible to tell how much progress a school has made.
If Band 1 is the Premier League of schools in Wales, we aren’t being told which is Manchester United and which is Wigan Athletic.
These plans have been informed by the termly stock takes and close working between the Welsh government’s school standards unit and local authority consortia”
WELSH GOVERNMENT SITE