Riding school discipline is a habit that comes with time (8)
I believe the answer is:
dressage
'riding school discipline is a habit that comes with time' is the definition.
'dressage' can be an answer for 'riding' (dressage is a kind of riding). I'm not sure about the rest of the definition.
'habit that comes with time' is the wordplay.
'habit' becomes 'dress' (I've seen this in another clue).
'that comes with' says to put letters next to each other.
'time' becomes 'age' (an age is a period of time).
'dress'+'age'='DRESSAGE'
Can you help me to learn more?
(Other definitions for dressage that I've seen before include "Mounted training" , "Method of horse training" , "Event for rider" , "discipline for horses" , "equestrian activity" .)