Many schools also have problems stopping parents taking children on term-time holidays, according to a report from inspection agency Estyn.
But very few schools are using government-provided benchmarking data to set targets for improving attendance, and in a minority policies are so out-of-date they are "not fit for purpose".
Estyn's new Improving attendance report highlights best practice in tackling truancy. It says LEAs that give a clear strategic lead to schools have been most successful in reducing truancy.
Taking a lead role, providing supporting materials, using data to target resources, expanding education welfare services and innovative use of funding all help.
The best-performing schools create an environment "that welcomes pupils and encourages them to attend". They also have a designated link governor and senior manager and good links with families.
But few schools are using Assembly government data comparing attendance rates to schools with similar intakes to set targets.
And truancy sweeps have only a short-term effect, unless combined with other measures addressing the underlying reasons for non-attendance, say inspectors.
Overall, absence rates have remained virtually unchanged for the last three years, at 9.4 per cent of half-day sessions missed. And a 2004 Assembly government target of reducing secondary school absence to below 8 per cent has still to be reached.
John Williams, head of Penydre comprehensive, which serves the Gurnos estate in Merthyr Tydfil, feels the curriculum is crucial.
"The traditional curriculum with its emphasis on more academic subjects held no interest for a certain percentage of children," he said. "By broadening this out to include more vocational subjects, we have made school more attractive to a larger number of children."
Working with Merthyr college and other organisations has allowed the school to provide 15 additional subjects.
Other methods used to increase attendance from 80 to 90 per cent over the past 10 years have included electronic registration, prizes and trips for 100 per cent attendance, and a Pop Idol competition. "It has been a slow process but we are making a determined effort," said Mr Williams. "This school has a remarkable staff of dedicated teachers committed to improving every aspect of the school. It is a total team effort."
Sue O'Halloran, head of Garth primary, Maesteg, also targeted attendance when she started there, and has seen the figures rise from below 90 per cent to 93.
Children with 100 per cent attendance records receive certificates each half-term, and gifts including cricket sets and jewellery-making kits for a whole year.
"It is a big incentive. We use the carrot rather than the stick," she said.
The school and other local primaries have been supported by the Llynfi Valley On-Track scheme.
Family support worker Julie Longley said: "It's vital to explain to children as soon as possible why coming to school is important.
"I always visit the infant classes and we do games and I make it fun. I also visit the homes of children who miss school and talk to the parents.
Once they are told how crucial school is, attendances usually improve dramatically."
Improving Attendance, see www.estyn.gov.uk