Schools should be judged on the performance of their pupils years after they have left education, the national schools commissioner has suggested.

Speaking at today’s Academies Show, Sir David Carter highlighted the gap between disadvantaged pupils and their peers, which he said was 18 months last summer.

He said: “It’s almost like saying to those children, ‘You are going to take your GCSEs in the October half-term of Year 10.’

“I think it’s our civil rights challenge in this country, to close this gap. I think it’s as important as that.”

Sir David said that multi-academy trusts had a key role in improving social mobility, particularly as many of their schools serve deprived communities.

‘The true test is what happens to pupils after school’

He suggested that the main measure used by the government to assess the performance of secondary schools, Progress 8, was not enough to judge their impact on disadvantaged pupils.

He said the creation of a new measure, which would examine where their former pupils were aged  25, could help.

“We can’t simply measure the improvement by a set of Progress 8 scores in GCSE,” he said. “We have to able to look more broadly than this at what kind of experience are we giving youngsters.

“I spoke at an IOE [Institute of Education] conference about six weeks ago where the question from the audience was, ‘If you could change one thing, what it would be?’

“The change I suggested we consider is what would it be like to have a new metric that looked at the performance of young people when they reached their 25th birthday, as opposed to being in our school system at 16 or 18, because the true test of the quality of your leadership is about what happens to those children afterwards.

“I think that’s one of our challenges in looking at vulnerable communities.”