Nearly half a million children could be starting their GCSEs this week without getting any support from the flagship Covid catch up scheme.
Labour analysis found that 490,800 Year 11 pupils were estimated to have missed out on help from the National Tutoring Programme this year.
Boris Johnson promised personal tutoring provision to help children catch up after the pandemic wreaked havoc on their learning.
But the roll out has been criticised for failing to reach poorer pupils who were already behind their wealthier classmates before the pandemic hit.
A recent report by the Commons Education Committee warned that disadvantaged children could be up to eight months behind at school due to Covid disruption and catch-up plans are failing to get to them.
Shadow Schools Minister Stephen Morgan warned that the "inadequate" catch-up plans risk cementing the widening the attainment gap.
He said: “This Government’s miserable failure to address Covid lost learning has left thousands of students to sit this years’ exams without the support they need.
"Ministers’ inadequate education catch-up efforts have wasted public money and now risk cementing the widening gap amongst young people.”
Around 1.2 million tutoring courses have been started since the programme launched in November 2020, with around 900,000 this academic year.
Education Secretary Nadhim Zahawi wrote to heads to urge them to use the scheme “as soon as possible” after the Department for Education estimated 40% of schools had not offered any sessions this year.
In his letter, the Tory schools chief said: “I appeal now, in particular to those schools that have not yet started to offer tutoring, to make sure that you do so as soon as possible this term.
“Do not miss out on an opportunity to help pupils who could benefit now."
Unions accused the Government of trying to “name and shame” schools by vowing to publish the data in the autumn and share it with Ofsted.
Dutch company Randstad lost the contract for the scheme for next year after being criticised by schools for issues with bureaucracy and difficulties with using the online portal.
A Department for Education spokesperson said: “There have been 1.2 million courses started as part of the National Tutoring Programme – transforming the way schools support children and young people who need it most. Schools continue to identify pupils who require support and parents that believe their child is eligible for tutoring should raise it with the school.
“We recognise young people sitting exams have faced disruption, which is why we have worked with Ofqual to put in place a range of adaptations – including advance information on some exam content – to maximise fairness and support students.”
