There was a sustained north-south divide for GCSE results in England this year, according to analysts.
SchoolDash said that while from 2011 to 2013 the gap between north and south was about 2.5 percentage points at GCSE, in 2014 it jumped to 4.8 percentage points.
Preliminary results for 2015 released by the Department for Education show a 4.6 percentage point difference.
The education data firm said this shows the "gap was more or less sustained, indicating that the 2014 increase was not just a blip" and puts the difference down to deprivation.
The company defines schools in the north as any in the North East, North West, Yorkshire and The Humber, the East Midlands and the West Midlands.
The South refers to schools in the South West, South East, London or the East of England - which it said was effectively a divide that is very close to a straight line drawn between the Severn Estuary and The Wash.
It pointed out that at A-level there is a north-south attainment difference of about three percentage points, but no clear gradient along the length of the country, with the North West performing well and the South East doing poorly.
SchoolDash said a clear north-south divide can be seen during the first three years of children's schooling in maths, reading and writing at the end of Key Stage 1.
It added that the North East has improved its writing attainment over the last few years, but not maths or reading.
The difference does not continue into Key Stage 2, when "the north-south difference has been all but eliminated" and the best-performing regions at this stage are London, the North East and the North West.
As other research has found, although London, like the north, has high levels of deprivation, children are performing better there.
Separate research published in September showed the proportion of children on free school meals in inner London who obtained five or more A*-C grades at GCSE has more than doubled over a decade.
The report, compiled by researchers associated with the London School of Economics (LSE) and Institute for Fiscal Studies (IFS), said improvements in primary schools played a major role in later boosts in secondary schools while the capital is also much more ethnically diverse than the rest of England, and ethnic minorities tend to achieve better GCSE results than children from white British backgrounds.
SchoolDash said: "London has now completely bucked the trend: it has very high levels of deprivation but also quite high levels of attainment.
"In contrast, northern regions have if anything got worse, even allowing for their higher levels of deprivation.
"In summary, regional performance at seven-years-old seems to correlate closely with deprivation, except in London, which does unusually well.
"Between seven and 11-years-old, northern schools tend to make better progress, but once those kids go to secondary school their average performance falls well behind their compatriots in the south."