By Sean Coughlan BBC News Online education staff

Tony Blair announced his plans in Southwark, one of the targeted authorities

The prime minister is getting tough on failing schools in inner London, saying that too many children are missing out on a decent education.

But although Tony Blair's announcement on Monday was billed as the most radical shake-up of London schools for 60 years, it certainly was not the first.

And teachers' unions were quick to point out that these authorities had already been at the receiving end of previous "radicalism" and that progress has not always been evident.

Since coming to power in 1997, Labour has constantly returned to the theme of tackling the deep-seated underachievement of inner-city schools, with a series of initiatives and interventions.

And in inner London the problems of urban education seem particularly acute, with exam results much lower and truancy much higher than the national average.

But so far repeated initiatives have struggled to make a significant impact on standards which the prime minister has conceded remain "unacceptably low".

Among the first attempts was the "education action zone" scheme, which particularly targeted funds and local community involvement at schools in deprived areas.

Although commended for developing innovation, these zones have been widely seen as not making the big impact that was anticipated.

Failing authorities

When individual local authorities were seen as problematic, the government gave itself powers to take over failing services and contract them out to the private sector.

Although this was seen as a ground-breaking move for a Labour government, the results have been less of a breakthrough.

Among the five London authorities targeted by the latest initiative, Islington has a privately-run education service, which has been fined for failing to achieve exam targets.

And in Southwark, the private contractor last month ended a five-year contract after only two years.

The latest tough message on failing schools included a threat to close those which do not show signs of improvement.

But this has already been attempted on long-running under-performing schools, under the "fresh start" scheme.

'Superheads' fade away

This promised that failing schools would be closed and would then re-open with a new name, a fresh coat of paint and an inspiring "superhead", who would provide successful leadership.

Except the problems often proved much deeper-rooted than had been anticipated, with the problems of the schools' intake more difficult to change than its name.

Torsten Friedag, the first "superhead" at the re-named Islington Arts and Media School, was appointed and then resigned in a blaze of publicity.

More recently, the Excellence in Cities scheme has renewed the focus on raising standards in inner-city schools - putting more resources into the capital's schools.

And city academies, which are autonomous state-funded schools, are to be increased in number, with the ambition of building centres of excellence in deprived areas.

But as the prime minister highlighted, results in these struggling authorities are well-below average, and in the capital's worst secondary schools, less than a quarter of pupils are leaving with five good GCSEs.

If successive initiatives have struggled, it could reflect the complex problems facing schools in the poorest areas of London.

Sink schools

Compounding the underachievement associated with poverty, there are other factors that produce so many "sink" schools in the capital.

Parents can send their children across local authority boundaries, and the most motivated parents push their children towards the most successful schools - and away from the least popular schools.

Many pupils in struggling authorities will travel to "better" schools in other authorities - leaving unpopular and unsuccessful schools with a shrinking number of the most able or most motivated pupils.

This has given London many of the best schools in the country - and also many of the worst.

Another distinctive aspect of London education is the high number of pupils taught in independent schools - taking more middle class parents out of the state system.

In some inner-London authorities, this can mean up to 40% of pupils either going private or travelling to state schools in other boroughs.

Inner-London schools have also faced a particular problem with many temporary and overseas staff - and the student population can also be much more transient than elsewhere in the country.

And social problems, connected with deprivation and "dysfunctional" families, have often been seen as being more concentrated in the poorest London boroughs than elsewhere.

As the Education Secretary Charles Clarke says: "There are still far too many schools which are failing to inspire and lead their communities. Too many parents are anguished and fearful rather than proud and confident when choosing their child's secondary school."

And the problem set out by the education secretary will not be easy to resolve.