The prime minister has promised schools in England there will be more money "coming down the track" after catch-up plans were labelled a "damp squib".
Head teachers had said they were "hugely disappointed" by a £1.4bn Covid recovery package, which breaks down to £50 extra per pupil per year.
Most of the funding will be for tutoring to make up for lost learning.
Boris Johnson said it would "give parents the confidence" that their children would be supported.
But the plans so far are much more limited than the £13.5bn that the Education Policy Institute (EPI) think tank had calculated would be required to catch up on lessons disrupted by the pandemic.
The catch-up plan, with £1.4bn extra over three years in addition to the £1.7bn already announced, will include £1bn for 100 million hours of tutoring and £250m for teacher training and development.
Tutoring, often in small groups, will be targeted at those considered most in need of support, particularly the disadvantaged and will not available for all pupils.
The EPI, which warned primary pupils had lost up to two months of learning in reading and three months in maths, said the extra funding amounted to £50 per pupil per year - a tenth of what it estimated was needed.
Spread over three years, the extra cash is worth about 1% of the annual schools budget, said the EPI.
The support was lower than in other countries, said the think tank, with catch-up funding in England, including earlier announcements, worth £310 per pupil over three years, compared with £1,600 in the United States and £2,500 in the Netherlands.