State school that's going places very quickly (7,5)
I believe the answer is:
express train
'that's going places very quickly' is the definition.
(express trains go fast)
'state school' is the wordplay.
'state' becomes 'express' (synonyms).
'school' becomes 'train' (training is a kind of schooling).
'express'+'train'='EXPRESS TRAIN'
(Other definitions for express train that I've seen before include "Rapid means of transport" , "occasionally halting transport" , "Fast form of transport" , "Speedy transport" , "This should get you there quicker" .)