The story of England's education system is "a tale of two nations", Ofsted warned today.
Children from similar backgrounds and of similar abilities can end up with different prospects just because of where they were born and the quality of the school they attended, according to the watchdog's annual report.
It suggested that there is still a "patchwork of provision", with some areas performing much better than others.
"There are disadvantaged areas that provide an excellent education and affluent regions that could do much better", the report says.
Overall, the performance of the nation's primary schools has improved, Ofsted found.
There are now three areas where fewer than 60% of primary-age pupils attend a good or outstanding school, compared to 23 last year.
And many local authorities that had under-performing primaries have made "significant progress", it added.
In Coventry, the proportion of pupils attending a good or better primary school has risen from 42% to 64%, while in Derby it has gone from 43% to 69%.
But Ofsted also warned that improvement had not been seen across the board, with the proportion of pupils attending a decent primary in Southend-on-Sea falling by six percentage points while in Bracknell Forest it fell by eight percentage points.
Overall, 97% of pupils in Darlington are in a good or better primary school, along with 95% in both Bedford and Windsor and Maidenhead.
At the other end, around 56% of Wolverhampton pupils go to a decent primary, along with 59% in both Medway and Thurrock.
The report also concluded that the picture is poorer in secondary schools.
In total, in 13 authorities less than half of secondary-age pupils were in good or outstanding schools. Of these, five are in the Yorkshire and Humber region.
But there are nine areas, where every pupils attends a good or better secondary school. These authorities are Bath and North East Somerset, Camden, Hammersmith and Fulham, Hounslow, Islington, Kensington and Chelsea, Rutland, Tower Hamlets and Westminster.
At the bottom of the scale, just 14% of pupils on the Isle of Wight go to a good or outstanding secondary school, along with 22% in Barnsley.
"Even were circumstances are relatively benign, poor leadership and teaching can conspire to deliver a mediocre education," Ofsted's report said.
"Take the East of England, an often attractive and largely rural area not commonly associated with educational failure. Children in this region have among the lowest chances in the country of attending a good or better school."
Chief inspector Sir Michael Wilshaw said: "It is not an exaggeration to report that the story of our schools and colleges today is a tale of two nations.
"Children from similar backgrounds with similar abilities, but who happen to be born in different regions and attend different schools and colleges, can end up with widely different prospects because of the variable quality of their education."