Prepares for performance by practice (6)
I believe the answer is:
trains
'prepares for performance by practice' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for trains that I've seen before include "Locomotive-drawn rail cars" , "Prepares for competition" , "schools" , "Aims; coaches" , "They're choo-choos to children" .)