The average pupil in some parts of Wales is missing a year of schooling through poor attendance and truancy.
Rhondda Cynon Taf council has launched a crackdown in an attempt to raise children's standards of achievement.
Its data shows that of the 12 years of statutory schooling, the average pupil only attends classes for 11 years.
Last month, education minister Leighton Andrews said there would be zero tolerance of truancy in future.
The council said if children had good attendance levels they were likely to achieve better exam results:
"Poor attendance and punctuality means bad grades and the effects of it can last a lifetime. It is vital that children and young people are
given the best education possible. To achieve this, all children need to
attend school regularly, with non-attendance being unacceptable. If a child is 15 minutes late for school a day, it means the equivalent of losing two weeks of school per year. Missing a school day a week is the same as losing a quarter of the year's education."