By Sean Coughlan BBC News Online education staff

Parents want their children to have the best chance

A few years ago, there was a scheme to revitalise struggling schools called "fresh start".

This promised schools in deprived areas extra money, a fresh sense of purpose and purge on the negativity that accompanied decades of underachievement.

And a London head teacher of one of these flagship schools, in one of the capital's poorer corners, said that despite this mood of optimism, he had heard a parent saying the best way of improving the school would be to take a bulldozer and flatten it.

It seemed absurdly pessimistic - and ran against the assumption that with enough effort, cash and good leadership, any school could be turned around.

If you went to that school today, you would find that the parent was a better judge - the classrooms are empty and the school is closed down, as the fresh start succumbed to a much more deep-rooted sense of failure.

Highest and lowest

London schools have continued to make the headlines - for good and bad reasons. When this year's school league tables are published this week, it is safe to assume that London boroughs will be among the highest achieving authorities in the country.

A third of inner-London pupils are not taught in their own borough's schools

Parents will be fighting for places for their children in these top ranking schools, buying their way into the right catchment areas to the extent that �50,000 can be added to local house prices.

But travelling a few miles across the capital can give parents a completely different problem - how to find a good place for their children in authorities which are among the lowest-performing in the whole country.

Left-wing Hackney MP, Diane Abbott, highlighted the conscience-pricking difficulties facing parents when she sent her son to a private school, rather than to a local comprehensive.

But how can such extremes exist between boroughs in such close proximity? And how can schools facing similar levels of social problems generate such different results?

There have been no shortage of attempts to tackle the problems of inner-city areas such as London. Action zones, fresh start and excellence in cities have all looked for ways of reversing out of a long record of underachievement.

'Unremitting' pressure

The Prime Minister Tony Blair launched the latest attempt to tackle failing London schools with an "unremitting focus" on five authorities - Hackney, Haringey, Islington, Lambeth and Southwark.

Diane Abbott is sending her son to a private school rather than a Hackney comprehensive

The education services provided by several London boroughs have been deemed so beyond repair that control has been taken away from education authorities and outside contractors brought in.

In some areas, the problem for parents might not only be finding a good school for their children, but finding out who is running their schools.

In Southwark, the second lowest scoring authority in last year's primary league tables, a private contractor was brought in to replace the local authority. But that contractor also pulled out and another interim body has taken over ... until next year, when another organisation will be appointed.

The perceived successes and failures of authorities and schools have created a London school population that is highly mobile, with parents bringing their consumer instincts to the hunt for the right school.

Motivated families

This chase for places affects both the inner city and leafier suburbs. Within the five targeted inner London authorities, a third of pupils go private or travel away to school in another borough.

This often means that the most motivated families are opting out of local schools, which becomes a problem in itself, leaving behind empty school places and creating an intake deprived of many of the most ambitious families.

But it isn't a simple case of the poorest boroughs losing pupils to schools in more successful authorities.

Richmond-upon-Thames has in recent years topped the primary league tables - and it might have been expected that the most successful pupils in the country, aged 11, would continue to produce strong results in secondary school.

But pupil mobility can work in many different directions - and over a quarter of families in Richmond opt out of the state system entirely and send their pupils to private secondary schools.

There are other Richmond families that send their children to other authorities - so that in practice, about 40% of pupils taught in Richmond secondary schools are from other boroughs.

This shifting intake might explain how the secondary school system in Richmond produces only average results, while its primary schools can claim to have the best test scores in the country.

And while an authority such as Hackney might be stereotyped as an example of blighted, inner-city education, in practice, some of its secondary school results are not dissimilar to struggling schools in Richmond.

Taking these boroughs as examples, it is also possible to see the social extremes that contribute to their differences in academic achievement.

Hackney is one of the poorest areas of the country, Richmond is one of the richest. In Hackney, 80% of pupils are from ethnic minorities, in Richmond the figure is 14%.

But as in Richmond, many pupils from Hackney are crossing London to go to schools in other boroughs, their parents chasing what they hope will be a better chance.