Rate gets school deep trouble (5)
I believe the answer is:
speed
'rate' is the definition.
(I know that speed is a type of rate)
'school deep trouble' is the wordplay.
'school' becomes 'S'.
'trouble' indicates anagramming the letters.
'deep' is an anagram of 'peed'.
's'+'peed'='SPEED'
'gets' acts as a link.
(Other definitions for speed that I've seen before include "Rate of travel" , "Pace or tempo" , "Velocity" , "'More haste, less . . . . .'" , "Travel quickly" .)