Thousands of children were regularly missing from Doncaster's schools during the first two terms last year, new figures reveal.
Across the country, absence rates have increased over each of the last two years, following several years of general improvement.
The National Education Union said that the “exam factory culture” in schools is causing disengagement among pupils.
Department for Education numbers show that 18% of state secondary pupils in Doncaster were classed as persistently absent in the autumn 2017 and spring 2018 terms, meaning they missed at least one in ten classes.
When primary schools in the area are included, 14% of pupils across the 120 state schools were persistently absent.
In line with the national trend, it is an increase on the previous year.
On average, pupils missed six days of school, which equates to 5% of their teaching time.
Authorised absences, such as for illness or medical appointments, accounted for 64% of time off. The remainder was unauthorised, including truancy and family holidays for which permission was not granted.
In total, Doncaster's state schools lost 237,000 days of teaching during the two terms.
Across England, 14% of students in state secondary schools and 10% in primary were persistently absent.
Nansi Ellis, assistant general secretary at the NEU, said: "Pupil absence is a serious issue but not necessarily one for which there is an easy or quick solution.
"Teachers understand that the curriculum plays a major role in engaging young people and reducing disruptive behaviour. The exam factory culture in our schools however is a significant contributing cause of children and young people’s mental health problems and disengagement in school life.
"We need a curriculum that gives every child the education they deserve and makes education the fulfilling joyous experience it should be."
A DfE spokesman said: “No child should be taken out of school without good reason – children only get one chance at an education and evidence shows that every extra day of school missed can affect a pupil’s chances of achieving good GCSEs.
"While the number of absences has risen slightly, they are still far below the rate seen in schools ten years ago.
"The rules on term-time absences are clear and we have put schools back in control by supporting them – and local authorities – to use their powers to deal with unauthorised absence."
Local councils can impose fines of £60 on parents who fail to ensure their children's attendance at school, rising to £120 if not paid within 21 days.