London pupils outperformed the rest of England in this year's tougher primary school tests, with a 28 percentage point gap between the best and worst performing local authorities.
In the London borough of Richmond, 67% of 11-year-olds reached the required standard in reading, writing and maths, according to provisional results.
But only 39% of 11-year-olds in Peterborough met the standard.
Head teachers' leader Russell Hobby said it indicated a system in chaos.
Schools minister Nick Gibb said the majority of pupils had performed well, adding that he wanted this success "to be the standard".
This year's tests, taken by 11-year-olds in England in May, were more demanding than those in previous years and based on a new curriculum.
Overall, just over 53% of children in state-funded schools met the grade in all three sets of tests.
In 2015, 80% met the standard - but those figures are not regarded as being comparable because they were under the previous system that was dropped this year.
Last year, under the old system, the gap between the highest performing areas, at 90%, and the lowest, at 73%, was narrower than this year.
The detailed provisional figures for this year show the highest performing local authorities concentrated in London, and parts of the North East and South East.
The poorest performing are in the West Midlands, Yorkshire and the Humber, the East Midlands and East of England.
This is a similar spread to that seen in recent years, according to the government statistical release, which also points out that that there was a small number of local authorities with "more extreme values".
Making the grade by region
- North East 56%
- North West 52%
- Yorkshire and The Humber 49%
- East Midlands 50%
- West Midlands 49%
- East 52%
- London 57%
- South East 54%
- South West 51%