Student acted strangely (5)
I believe the answer is:
cadet
'student' is the definition.
(I have seen 'Military student ' mean 'cadet' so perhaps 'student' could also mean 'cadet')
'acted strangely' is the wordplay.
'strangely' is an anagram indicator.
'acted' is an anagram of 'CADET'.
(Other definitions for cadet that I've seen before include "not the heir" , "recruit" , "Police or armed forces trainee" , "aspiring officer" , "Young trainee, eg in the police" .)