Plan in school: English supported by the writer (6)
I believe the answer is:
scheme
'plan' is the definition.
(scheme is a kind of plan)
'school english supported by the writer' is the wordplay.
'school' becomes 'sch'.
'english' becomes 'e' (abbreviation).
'supported by' says to put letters next to each other (letters go below - in down clue).
'the writer' becomes 'me' (the person who is writing these clues).
'sch'+'e'+'me'='SCHEME'
'in' is the link.
(Other definitions for scheme that I've seen before include "Machination" , "Plan, ruse" , "Lay plans" , "Secret plan, plot" , "Plan (maybe best laid?)" .)