Factor in school session with European journal (12)
I believe the answer is:
intermediary
'factor' is the definition.
(thesaurus)
'in school session with european journal' is the wordplay.
'school session' becomes 'term' (I've seen this before).
'with' says to put letters next to each other.
'european' becomes 'e' (abbreviation e.g. EU).
'journal' becomes 'diary' (diary is a kind of journal).
'in'+'term'+'e'+'diary'='INTERMEDIARY'
(Other definitions for intermediary that I've seen before include "Agent" , "Go-between" , "Negotiator" .)