One skipping school (6)
I believe the answer is:
truant
'one skipping school' is the definition.
(truancy is skipping school)
This is all the clue.
(Other definitions for truant that I've seen before include "Delinquent" , "Pupil skipping school" , "Pupil away from school without leave" , "On the mitch" , "Academic absentee" .)