Silverdale looks like the classic comprehensive. A 1950s sprawl of ugly buildings and prefabricated classrooms, it stands on a hillside overlooking the industrial city of Sheffield.

At first sight it's not much more attractive on the inside. Parts of the school are a building site. It holds a third more pupils than it was designed to teach. Uniforms - when worn - are generally dishevelled. And yet the school buzzes with positive energy.

The pupils who show me round are fiercely proud of the school, their loyalty a testament to something unseen - the quality of the teaching and the school's distinctive ethos. Sixth former Laura Bennett, 17, would rather be here than at a private school, not least because she fears she wouldn't feel at home politically. Sheffield's Labour tradition, she says, is widely shared among Silverdale's students.

Then there's the education she's getting as well. "I think the teaching's very good here. The attitude of teachers is great and they put in a lot of effort for us."

The school is an ordinary comprehensive that has consistently managed to add value to a non-selective intake, producing outstanding results. Year after year it maintains its solid performance on the back of excellent teaching and an impressive student work ethic.

The school came in at 471st in the FT's top 1,000 schools league table this year, ahead of several dozen private schools. Entry into the FT's table places a school in the top league, above nearly 4,000 others. Its FT score of 18.9 points indicates an average achievement equivalent to A Levels of grades B,C and C.

About 95 per cent of Silverdale's sixth formers will go on to university this year, of which a handful have been accepted into Oxbridge.

But with several experienced teachers retiring, ever-increasing enrolments from ethnic minorities for whom English is not a first language (now 13 per cent of the student body), uninspiring facilities and overcrowding, the school cannot afford to rest on its laurels.

Helen Storey, the headteacher, attributes the school's success to the excellent teaching and subject knowledge of her staff and the fact that pupils are eager to learn.

Her comments echo the call of Tony Blair, the prime minister, now set out in a white paper on secondary education, that every school should strive to have an "ethos" of its own. Silverdale shows that such an ethos can be created in a non-selective comprehensive.

In its assessment of the school last year, Ofsted acknowledged the attributes spelled out by Storey, noting that they had made a significant contribution to the standards achieved. It also approved the school's ethos, which it saw as promoting good attitudes, behaviour and attendance in its pupils.

"The school promotes effective learning through good relationships between teachers and pupils and because teachers in Silverdale have a very good knowledge of the subjects they teach," the Ofsted report states. "The school's strengths outweigh its weaknesses and it provides good value for money."

Storey also attributes some of the school's success to healthy parental support, which derives partly from its location in a relatively affluent part of Sheffield.

The catchment area is wedge-shaped, with the broadest part falling in the leafy suburb of Bent's Green and tapering off into the inner city. This means the majority of pupils come from fairly well-off, middle-class families.

Silverdale has its shortcomings, though - not least the condition of its buildings. Pupils have somemtimes been sent home because of rising damp and unsafe roofing. Storey finds that lobbying for improvements is becoming an important part of her job.

Ofsted acknowledges this problem, noting that the library is too small to be an effective resource and that the lack of space is hampering its ability to introduce information technology and vocational studies.

Silverdale, nevertheless, attracts extra funding on several fronts. It is a "Beacon" school - chosen to spread best practice. As such, it has developed several popular bridging units in English, mathematics and science for pupils transferring to the school, expanded links with teacher training institutions, and developed a good mentoring system.

Involvement in the Excellence in Cities project has also enabled the school to offer a much wider variety of extracurricular activities as well as obtain two mentors for under-achieving pupils.

The money these bring in is welcome but limited. Storey feels that if substantial funds are to be found a more radical approach may be required, for instance seeking specialist school status or private sponsorship.

"Unless we have some long-term commitment to developing the buildings - creating better science labs, for instance - it's going to be difficult to improve performance, which we have the potential to do. Ultimately we could see a decline because we're overcrowded," she says. "We can't assume we can keep on doing what we've been doing for the past five years."

So far Silverdale has had no trouble finding competent teachers to fill vacant posts. The school's good academic results keep staff motivated and are the main reason why it has been able to hang on to good teachers. Storey is frustrated, however, at not being able to improve their working environment by creating, say, a staff work room with a few computers. She believes that unless something is done to improve teachers' working conditions and to raise the profession's status, teacher shortages will continue to plague the school system.