Ruffwood comprehensive in Knowsley has called for the prosecution of parents who condone truancy. Condoned absence has historically been a large problem for the school.
Giles Elliott, the headteacher, said: "There isn't a culture of valuing education in this area. It would be easy for us to take the sick notes and not go any further. But we need to take a hard line."
Parents, he said, often kept children home to look after younger siblings.
Recently, a mother attempted to persuade teachers that her daughter had a dental appointment every Monday and Friday for five weeks.
"Parents were siding with children," Mr Elliott said. "It's a cultural thing. The national curriculum was very academic and straitjacketed, so it has never been relevant for these children."
This year's Department for Education and Skills league tables showed that the proportion of half-days missed through unauthorised absence at Ruffwood was 10.5 per cent: the highest in England where the average is 1 per cent for secondaries. In June last year, Knowsley borough council convened a panel to examine Ruffwood truancy. Twenty-five families have appeared before this panel, with 24 children showing a marked improvement as a result. Eight Ruffwood families have been prosecuted.
Authorised absence has fallen to 9.3 per cent of half days. And, since August, when the tables were compiled, overall truancy has dropped 4 percentage points.
Steve Munby, Knowsley director of education, said: "Our priority is raising self-esteem and aspirations. We want to make the curriculum more relevant, by engaging young people in learning outside school. We're not accepting excuses any more."