Departed from school at Easter (4)
I believe the answer is:
late
'departed' is the definition.
(I've seen this before)
'from school at easter' is the wordplay.
'from' indicates a hidden word.
'LATE' is hidden in the letters of 'school at easter'.
(Other definitions for late that I've seen before include "Far on in the day" , "Yet to arrive?" , "Not yet arrived - departed" , "after the sell-by date?" , "Running behind time" .)