After the coronavirus pandemic wreaked havoc on children's education, the number of pupils missing school without permission has risen significantly since before Covid-19, new figures show.
The Association for School and College Leaders said attendance is "one of the biggest challenges" schools must face, with several complex factors contributing to the problem.
Department for Education figures show 301,000 of 18.5 million school sessions were missed without permission by pupils in Hampshire.
It meant children in the area had an unauthorised absence rate of 1.6%.
The school day is split into a morning and afternoon session, with every child expected to attend all sessions.
In the 2018-19 spring term, the unauthorised absence rate was 0.9%, meaning it has increased by 78% during the coronavirus pandemic.
Nationally, 2.3% of pupils missed school without permission in the spring, almost double the 1.2% who were absent from lessons in 2018-19.
Every area in the country has seen the rate of unauthorised absences rise by more than 30% since 2018-19.
Julie McCulloch, director of policy at the ASCL, said there are several complex factors causing rising absence rates.
They include mental health issues, exacerbated by the pandemic, a lack of support for children with special educational needs, with schools lacking resources to deal with them, and the cost-of-living crisis, with 30% of children growing up in poverty, Ms McCulloch added.
She said: "It will take concerted government action to address these issues, all of which are linked to high levels of pupil absence, and ensure all children are getting the support they need at the right time."
The overall absence rate has also risen across the country, from 4.8% in the 2018-19 spring term to 7% last year.
In Hampshire, 1.2 million school sessions (6.7%) were missed in the latest spring term.
A Department for Education spokesperson said: "The vast majority of children are in school and learning, and we are taking action to increase attendance because it is vital for a child’s education, wellbeing and future life chances.
"We have expanded our attendance hubs, which will support over 400,000 pupils across 14 hubs and provided a toolkit for schools about communicating with parents on this issue.
"Our mentoring programme, delivered by Barnardo’s, sees trained mentors work directly with 1,665 persistently and severely absent children and their families to understand and overcome the barriers to attendance and support them back into school."