Pretentious school clothing's in the van (6)
I believe the answer is:
kitsch
'pretentious' is the definition.
(synonyms)
'school clothing's in the van' is the wordplay.
'school' becomes 'sch' (abbreviation).
'clothing' becomes 'kit' (I've seen this in other clues).
'in the van' is a charade indicator (letters next to each other) (some letters go in the van ie at the front).
'sch' after 'kit' is 'KITSCH'.
(Other definitions for kitsch that I've seen before include "Poor taste" , "Garish tasteless art" , "Vulgar, sentimental, art" , "Tacky" , "Lack of good taste in art" .)