The inspectorate found that there were "exceptional pupil movements" at 340 settings, compared with previous analysis which identified 300 schools where off-rolling was suspected of happening.
Looking at the school census, the latest research compared pupil movements between year 10 and 11 in the 12 months to January 2018.
On average, 13 pupils left each of these schools "at a critical stage in their education", Ofsted's chief statistician Jason Bradbury writes in his blog published this month.
Of the 20,000 pupils who left all schools between year 10 and 11, 22 per cent were in one of the identified schools.
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Some 60 per cent of the schools on the previous watch list appear on the updated one, states Bradbury, with many of the settings which did not qualify, still losing pupils.
After the previous year's figures for 2016/17 were published, Ofsted condemned the practice of informally removing pupils with special educational needs and disabilities (SEND) from the roll.
Bradbury states: "The increase in the number of schools with exceptional pupil movement does not necessarily mean that off-rolling is increasing.
"There may be legitimate reasons for the increase in pupil movement.
"However, the increases do warrant further consideration."
He adds that "we do not know the destination" for about 10,000 pupils, because they left the state-funded sector and "we're unable to track them with the data currently available".
"Unfortunately, we do not have data on pupils who become home educated (and cannot be tracked)."
In April, the government unveiled proposals to require local authorities to create and maintain a register of home-educated children.
The Department for Education consultation, results of which have yet to be announced, followed calls from children's commissioner for England Anne Longfield, who found levels of home education had doubled in five years.
The National Education Union (NEU) is calling for the government to thoroughly investigate the "reasons for pupils no longer being registered at a school".
Dr Mary Bousted, the union's joint general secretary, described off-rolling levels as "extremely worrying".
"It is a tragedy when any pupil misses out on education," said Bousted. "For many SEND pupils and their families, leaving mainstream education becomes a reality when the underfunded system can no longer safely support them.
"The spike in off-rolling figures for year 10/11 is no surprise as this is when SEND pupils in particular reach crisis points due to the pressures of the new GCSE exam structure and an inflexible curriculum.
"It is urgent that we move beyond the numbers, analyse the real reasons behind these moves, and challenge the government policies which are undermining inclusive and high-quality education."