A child's chances of receiving a decent education continues to depend on where they live, with some areas still failing to close the gap between rich and poor pupils, inspectors have warned.

A new Ofsted report reveals that there remains "considerable variation" across local authorities in the proportion of youngsters achieving the expected standards at age 11 and 16.

Although some areas have seen major improvements, others are improving too slowly, the schools' watchdog said.

The study examined the use of the Government's pupil premium - extra cash given to schools to help disadvantaged pupils.

In 2014/15, the scheme will be worth £2.5 billion, which means that an average-sized secondary school with an average number of eligible pupils - those on free school meals - will receive around £200,000 in premium funding.

This is the equivalent of five full-time teachers, Ofsted said.

The report, based on official data and inspection reports, concludes there is evidence that the pupil premium is boosting the education prospects of many children.

It says that while it is still too early to tell if there has been a significant narrowing of the gap between rich and poor youngsters nationally, inspectors believe that school leaders are spending the extra money more effectively than ever.

The cash is most frequently being used to pay for extra teachers and teaching assistants who give individual help or small group tuition, usually in English and maths.

Ofsted chief Sir Michael Wilshaw said that the improving situation could be down to the watchdog looking at how the premium is being spent as part of inspections, and headteachers being aware that they cannot get a decent Ofsted judgment if they do not show how they are improving the results of disadvantaged pupils.

But the report also warned that some areas are performing better than others.

"Although inspectors have seen large improvements in the attitude of school leaders and governors, there is considerable variation across local authorities in the proportion of pupils achieving expected levels at Key Stages 2 (end of primary) and 4 (GCSE level) and the rate of improvement from year to year," the report said.

Pupils who are eligible for free school meals in Barnsley, Portsmouth, South Gloucestershire, North Lincolnshire and Northumberland were least likely to get five good GCSEs, including English and maths, inspectors said.

Last year, around one in four eligible pupils in these areas reached this benchmark, Ofsted said.

At the other end of the scale, Kensington and Chelsea, Westminster, Southwark, Tower Hamlets and Lambeth had the highest proportions of eligible youngsters - around three-fifths - reaching this standard.

The report goes on to note that Barnsley had the third lowest proportion of eligible children getting five or more C grades in 2012, and attainment has declined further to make it the lowest attaining authority in 2013.

It later concludes: "It cannot be right that the likelihood of a child receiving a good education should depend on their postcode or economic circumstance.

"Government should focus its attention on those areas of the country that are letting poor children down. Ofsted will also focus its attention on these areas in subsequent reports to see if improvements have been made."

Sir Michael said: "One of the greatest challenges this country faces is closing the unacceptable gap that remains between poorer children and their better-off classmates when it comes to educational outcomes.

"As chief inspector, I am passionate about improving the prospects of our least advantaged children so I am encouraged by the clear signs in today's report that more effective spending and monitoring of the pupil premium is starting to make a positive difference in many schools."

Schools minister David Laws said: "The pupil premium is transforming the life chances of pupils across the country, helping to build a stronger economy and a fairer society.

"This report shows that our reforms to make schools more accountable for how they spend the funding is revolutionising the way such pupils are given the best possible start to life. It shows headteachers, teachers and governors are rallying behind the policy to close the achievement gap between disadvantaged pupils and their peers. And where performance is an issue we are taking swift action to ensure all pupils are given the education they deserve."

Deputy Prime Minister Nick Clegg said: "The pupil premium has been one of the most significant changes in our education system for a long time and is already closing the attainment gap by helping up to two million disadvantaged children get the support, education and skills they need to get on in life - whether it's through literacy classes, catch-up lessons or one-to-one tuition."