The persistent disadvantage gap in schools will be an "early challenge" for the next prime minister, researchers are warning.
Andy Burnham is set to succeed the outgoing PM, Sir Keir Starmer, later this month – and he will face challenges at home and abroad should he move into 10 Downing Street.
The Education Policy Institute (EPI) has set out what it says is a key domestic problem he needs to deal with – that achievement gaps between pupils from poorer backgrounds compared with those from richer homes remain wider than before the coronavirus pandemic at every phase of education from early years to post-16.
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February's Schools White Paper set a target to halve the disadvantage gap by the time children born under this government finish secondary school.
However, the EPI is warning this ambition is "moving further out of reach, not closer".
Data from its latest annual report also finds big regional differences in terms of closing the gap. London outperforms all other regions again in this respect, with schools in the West Midlands having the smallest gap across all phases.
But the South East and South West have experienced some of the largest increases in the gap since the pandemic.
"The finding presents an early challenge for the incoming prime minister, who inherits the government's aim of halving the disadvantage gap just months after it was set out," said the EPI.
Julie McCulloch, head of the research institute, branded the size of the gaps "a scourge on our society".
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"The government's ambitious target to halve this gap is right and welcome," she said. "However, the findings of EPI's latest annual report show that, on current trends, the distance between where we are and where the government wants to be is growing, not shrinking.
"The next prime minister inherits a clear pledge and a difficult starting position."
Ms McCulloch added that a "credible, long-term delivery plan" is needed.
The EPI recommends that all children get the same entitlements to funded hours of early education and care regardless of their family circumstances.
It adds that more investment is needed so children and young people with special educational needs and disabilities can be supported, while targeted funding is also required for disadvantaged people aged 16 to 19.
School leaders' union NAHT general secretary Paul Whiteman said: "These stark findings underline just how difficult it is for the government to shift the dial on the stubborn inequalities we see in children's educational attainment.
"The government's stated determination to tackle this, starting from children's early years, is laudable, and measures including family hubs and extending free school meals should help in the long run.
"It is vital the new prime minister shows sustained commitment to tackling disadvantage in all its forms and in all areas of the country."
The National Education Union also called for "significant investment" in the wake of the report.
General secretary Daniel Kebede said: "The gaps between haves and have-nots are widening, and a step change of significant investment is required to turn this around."
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