Drink in bed in school (6)
I believe the answer is:
scotch
'drink' is the definition.
(Scotch is an example)
'bed in school' is the wordplay.
'bed' becomes 'cot' (cot is a kind of bed).
'in' means one lot of letters goes inside another.
'school' becomes 'sch'.
'cot' going inside 'sch' is 'SCOTCH'.
'in' acts as a link.
(Other definitions for scotch that I've seen before include "Finish off" , "Put an end to, say rumour" , "providing nursery facility in school" , "Northern whisky" , "Alcoholic spirit" .)