Pupils are bunking off the same number of days as last year - an average of nearly three.
But authorised absence has gone up, meaning that overall non-attendance has risen from 9.4 to 9.8 per cent of half-day sessions, the equivalent of around 15 days per pupil aged 11-15.
Schools where a higher proportion of children are entitled to free school meals are more likely to have high non-attendance rates. And while boys are more likely to truant, girls are taking more authorised absence, where permission to be out of school has been given by a teacher for genuine reasons, such as illness.
Heledd Hayes, education officer with the National Union of Teachers Cymru, said the rise was worrying. But she was not convinced of the need for specific initiatives on absence - even though unauthorised and overall non-attendance remains higher in Welsh secondaries (1.7 and 9.9 per cent) than in England (1.2 and 7.9).
"It's up to each local authority area and school because the causes of absence vary, and probably the solutions do too," she said.
Truancy rates ranged from 0.4 per cent of half days missed in Flintshire, to 3.4 per cent in Cardiff. Independent school pupils bunked off the fewest number of half days (0.7), compared with 9.4 in special schools and 5.3 in mainstream institutions.
Absenteeism from secondary schools in Wales 20056, http:new.wales.gov.uktopicsstatistics?lang=en