A quarter of pupils in Cornwall state schools missed at least 10% of their lessons last year, new figures show, as the coronavirus pandemic caused havoc for many children's education.
The Association of School and College Leaders said schools work very hard to improve attendances but have received little support from local authorities due to government cuts.
It called on the Government to publish a "nationwide attendance strategy" to support struggling families and schools.
Department for Education figures show 17,528 out of 67,413 total pupils in Cornwall missed at least 10% of lesson time in the 2021-22 academic year.
It meant 26% of pupils were persistently absent – significantly up from 11.2% the year before and 11.6% in 2018-19, the last full academic year before the pandemic.
Meanwhile, the overall absence rate in Cornwall schools almost doubled from 4.3% to 8.3%.
Across England, 1.6 million pupils were persistently absent, more than double the 800,000 who missed at least 10% of their lessons in 2018-19.
The persistent absent rate sat between 10 and 12% in recent years but jumped to 22.5% in the last academic year.
The coronavirus pandemic was the primary reason for the significant rise in pupil absences.
Julie McCulloch, director of policy at the ASCL, said that while absence rates were affected by the pandemic, "attendance continues to be extremely challenging".
This is due to "escalating rates of poor mental health, poverty, and abuse and neglect, which are compounded by an erosion in the provision of local support services over the past decade," she said.
Ms McCulloch added: "Schools work very hard to encourage good attendance but have little support as local authority attendance services have also reduced as a result of government cuts. We need a nationwide attendance strategy which supports struggling families and schools."
The figures also show 120,000 pupils missed at least 50% of their lessons in England last year – up from 80,000 the year before and 60,000 in 2018-19.
In Cornwall, 1,174 pupils (2%) were severely absent throughout the academic year – up from 718 in 2020-21.
Ellie Mulcahy, director of research at think tank The Centre for Education and Youth, said the rise in pupil absence is "disturbing".
"We know that just a few days off school can have a serious impact on young people's later attainment," Ms Mulcahy added.
A Department for Education spokesperson said: "The vast majority of children are in school and learning.
"We work closely with schools, trusts, governing bodies, and local authorities to identify pupils who are at risk of becoming, or who are persistently absent and working together to support those children to return to regular and consistent education."