Tell class about Spanish article (6)
I believe the answer is:
relate
'tell' is the definition.
(as in to tell or relate a story)
'class about spanish article' is the wordplay.
'class' becomes 'rate' (class can mean to rank or rate).
'about' is an insertion indicator.
'spanish article' becomes 'el' (the definite article 'the' in Spanish).
'rate' enclosing 'el' is 'RELATE'.
(Other definitions for relate that I've seen before include "Narrate or associate" , "Tell (a story)" , "Make a logical or causal connection" , "Recite - marriage guidance organisation" , "link" .)