The number of children off school has more than doubled in the past academic year, compared to pre-pandemic levels.
On average, 16.3% of secondary school pupils were absent during 2021-22, up from 6.2% in 2018-19, Welsh government figures show. Absences of pupils from poorer backgrounds was higher.
School leaders said some pupils have "simply got out of the habit of regular attendance and never fully re-engaged".
The Welsh government said it spent £4m on its family engagement officer roles.
In primary schools, 11% of pupils were absent, compared to 5.4% pre-Covid.
