Avoid barely posting on Twitter when upset about school (6)
I believe the answer is:
eschew
'avoid' is the definition.
(I know that eschew is a type of avoid)
'twitter when upset about school' is the wordplay.
'twitter' becomes 'wee' (I am not sure about this - if you are sure you should believe this answer much more).
'when upset' says the letters should be written in reverse (in a down clue - set, written, up).
'about' indicates putting letters inside.
'school' becomes 'sch' (abbreviation).
'wee' reversed gives 'eew'.
'eew' enclosing 'sch' is 'ESCHEW'.
'barely posting on' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for eschew that I've seen before include "Avoid,shun" , "'Avoid, stay away from (6)'" , "'Avoid, keep away from (6)'" , "'Stay clear of, shun (6)'" , "Deliberately avoid" .)