Spoken greeting in school? (4)
I believe the answer is:
high
'school?' is the definition.
(high is a kind of school)
'spoken greeting' is the wordplay.
'spoken' indicates a 'sounds like' (homophone) clue.
'greeting' becomes 'hi' (hi is a kind of greeting).
'hi' sounds like 'HIGH'.
'in' is the link.
(Other definitions for high that I've seen before include "Oxford street - drunk" , "Going off - in great spirits" , "Drunk; anticyclone" , "Way up" , "Relatively great or specific elevation" .)