Nearly 10,000 children were regularly missing from Sheffield's schools during the first two terms last year, new figures reveal.
Department for Education numbers show that 15 per cent of secondary pupils in Sheffield 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, 13 per cent of pupils across the 163 schools were persistently absent.
In total, Sheffield's schools lost 386,000 days of teaching during the two terms.
In England, 14 per cent of students in state secondary schools and 10 per cent in primary were persistently absent.
Absence rates across the country have increased over each of the last two years, following several years of general improvement.
Nationally, authorised absences, such as for illness or medical appointments, accounted for 62 per cent of time off. The remainder was unauthorised, including truancy and family holidays for which permission was not granted.
Assistant general secretary at the NEU, Nansi Ellis, 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."
Parents can be fined £60, increasing to £120 if they fail to pay within three weeks, for taking their children out of school during term time without the headteacher's consent.
In Sheffield, a Freedom of Information request revealed 3,067 such penalty notices were issued during the 2016/17 academic year - a big increase on the 2,310 handed out the previous year but slightly less than the 3,146 in 2014/15.
Sheffield Council's guidance says that headteachers have the discretion to grant leave during term time but should only do so in 'exceptional circumstances'.
In a statement, the DfE 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."