Leading article by teacher (5)
I believe the answer is:
ahead
'leading' is the definition.
(to lead is to go ahead)
'article by teacher' is the wordplay.
'article' becomes 'a' (English indefinite article).
'by' means one lot of letters go next to another.
'teacher' becomes 'head' ().
'a'+'head'='AHEAD'
(Other definitions for ahead that I've seen before include "In the leading position" , "in van" , "advanced" , "at pole" , "Winning" .)