Drink after school dance (8)
I believe the answer is:
highball
'drink' is the definition.
(highball is a drink)
'after school dance' is the wordplay.
'after' says to put letters next to each other.
'school' becomes 'high' (high school is a kind of school**).
'dance' becomes 'ball' (ball is a kind of dance).
'high' put next to 'ball' is 'HIGHBALL'.
(Other definitions for highball that I've seen before include "Mixed drink served in a tall glass" , "Cocktail served in a tall glass" , "Beverage" , "Spirit and soda in tall glass - lob (8);" , "Whiskey and soda with ice" .)