To reform some gangs, you need to lecture a lot (3)
I believe the answer is:
nag
'need to lecture a lot' is the definition.
I can't judge whether this definition defines the answer.
'to reform some gangs' is the wordplay.
'to reform' indicates anagramming the letters (letters in a new form).
'some' means to look at the middle letters.
The centre of 'gangs' is 'ang'.
'ang' is an anagram of 'NAG'.
'you' is the link.
Can you help me to learn more?
(Other definitions for nag that I've seen before include "Constant worrier" , "Bother persistently" , "old trout?" , "Complain continuously like old horse" , "its head to name the pub" .)