Ms Longfield, from Otley, said the gap widened during the pandemic as thousands of Northern children from the most deprived communities fell further behind when their schools were closed and they were unable to access a laptop for remote learning.
Speaking at the Great Northern Conference, she said disadvantaged pupils are on average 18 months behind the rest of the class in academic achievement by the age of 16 and while that figure has increased by five months for children in the North East, it has only risen by two-and-a-half months for pupils in London.
Children on free school meals in the capital are four times more likely to “get a good maths and English GCSE” than their counterparts in the North and they are twice as likely to go to university, she added.
At the conference, she called on political leaders and businesses to support schools and ensure children from all backgrounds have the resources and opportunities they need to reach their full potential.
“For me, this is an education issue, but it is also an economic issue. If we want to boost the productivity of the North, we must invest in the workforce of tomorrow,” she said.
"Boosting opportunities and supporting education can make that transformational change, to help children to live in the place they want to live, near the communities and families they love, but also to have access to those opportunities.”
At the conference, Natalie Doherty, director of quality, curriculum and innovation at the Source Skills Academy, said businesses need to “invest in young people” and provide them with opportunities to help them get into work.
Chancellor Rishi Sunak announced in his Budget speech on Wednesday that the Government will help schools and colleges with education recovery after the pandemic with "almost £5bn” of catch-up investment.
But the additional £1.8bn cash – made available on top of £3.1bn already pledged – has come under fire, with Britain’s largest teaching union branding the recovery plan “inadequate”.
It comes after Sir Kevan Collins, the former schools catch-up tsar, quit his role in June after the amount ministers were prepared to invest in education recovery fell short of what he believed was necessary. He had put forward a recovery package of £15bn over three years.
Earlier this month, the Government published figures which show the gap between poorer students and their more affluent peers attending university has widened to the largest gap for 14 years.
Better-off pupils are still significantly more likely to go to university than their more disadvantaged peers and the gap between the two groups – 19.1 percentage points – is the widest it has been since 2005/06.
Data from the Department for Education (DfE) shows that 26.6 per cent of pupils in England who received free school meals (FSMs) at the age of 15 went on to university in 2019/20, compared with 45.7 per cent of those who did not receive meals.