School outside American station (6)
I believe the answer is:
euston
'station' is the definition.
(London train station)
'school outside american' is the wordplay.
'school' becomes 'eton' (famous UK public school).
'outside' indicates putting letters inside.
'american' becomes 'us' (abbreviation for United States).
'eton' going around 'us' is 'EUSTON'.
(Other definitions for euston that I've seen before include "Small restaurants" , "north London area" , "rail terminal" , "London rail terminus" , "trains here in London?" .)