Certain boys out to upset the routine ways (7)
I believe the answer is:
methods
'routine ways' is the definition.
'methods' can be an answer for 'ways' (method is a kind of way). I'm unsure of the 'routine' bit.
'certain boys out to upset the' is the wordplay.
'certain boys' becomes 'mods' (I can't justify this - if you can you should believe this answer much more).
'out' indicates putting letters inside.
'to upset' indicates an anagram.
'the' with letters rearranged gives 'eth'.
'mods' going around 'eth' is 'METHODS'.
Can you help me to learn more?
(Other definitions for methods that I've seen before include "Procedures for accomplishing" , "Procedure to accomplish something" , "Procedures, systems" , "Techniques" .)