Russian girl in school garden (4)
I believe the answer is:
olga
'russian girl' is the definition.
(I've seen this before)
'in school garden' is the wordplay.
'in' says the answer is hidden in the clue.
'OLGA' is hidden in the letters of 'school garden'.
(Other definitions for olga that I've seen before include "Could be Russian girl" , "Lady" , "Russian girl's name, anagram of ..." , "Slavic girl's name" .)