To play truant (be absent from school without permission).
play the wag
play hooky
To play truant; to avoid (informally: skip) school, work, or other dut …
go on the mitch
to skip school; to play truant
French leave
A departure taken quietly and unnoticed, without asking for permission …
take French leave
To leave quietly and unnoticed, without asking for permission or infor …
take liberties
To act on one's own authority, without asking for permission.