Ofsted is to send teams of inspectors into areas where high numbers of pupils are not getting a good education in a fresh bid to raise school standards.
In a series of targeted inspections, the watchdog will visit around five or six local authority areas in England over the next few weeks.
These are all areas where the proportion of children attending a good or outstanding school is well below the national average for England, Ofsted said.
It is understood that about 10% of schools in each area will face an inspection.
The move comes amid the watchdog's concerns that in some local authority areas, thousands of children are being denied a decent standard of education.
In his first annual report, published in November, chief inspector Sir Michael Wilshaw raised concerns about children facing a postcode lottery in gaining a decent education, with some having a less than 50% chance of attending a good school.
Sir Michael warned that there were still "stark inequities" in the system and a youngster's chance of attending a high-quality school is often too dependent on where they live. He pointed out that there is no link between access to a good primary school and how rich or poor an area is.
Inspectors will spend about five days in each area, with all visits due to be carried out before the end of the spring term. Ofsted said the inspections would be carried out "without fear or favour, and with no preconceived idea of what we will find".
In a speech to the North of England Education Conference in Sheffield, Sir Michael will also set out plans for Ofsted to begin inspecting the school improvement service offered by local authorities under a new framework. If the new wave of targeted inspections reveals evidence that a local authority is not showing effective leadership of schools then it could be inspected under this new framework.
The first local authority to be visited will be Derby, Ofsted said. Inspections begin on Thursday.
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