Stiff class attended by a learner (6)
I believe the answer is:
formal
'stiff' is the definition.
('formal' can be similar in meaning to 'stiff')
'class attended by a learner' is the wordplay.
'class' becomes 'form' (form class is a kind of class**).
'attended by' says to put letters next to each other.
'learner' becomes 'l'.
'form'+'a'+'l'='FORMAL'
(Other definitions for formal that I've seen before include "Cermonial, solemn" , "Ceremonial; ordered" , "Conventional - ceremonious" , "Official; stiff" , "Essential" .)