Just outside gym for all to see (6)
I believe the answer is:
openly
'for all to see' is the definition.
(out in the open)
'just outside gym' is the wordplay.
'just' becomes 'only' (synonyms).
'outside' indicates putting letters inside (some letters go outside others).
'gym' becomes 'pe' (short for Physical Education).
'only' placed around 'pe' is 'OPENLY'.
(Other definitions for openly that I've seen before include "(Done) without concealment" , "In public" , "Above board" , "Overtly" , "In full view" .)