Students have difficulty getting Marxist concept (5,8)
I believe the answer is:
class struggle
'marxist concept' is the definition.
'students have difficulty getting' is the wordplay.
'students' becomes 'class'.
'have' means one lot of letters go next to another.
'difficulty getting' becomes 'struggle' (I can't justify this - if you can you should give a lot more credence to this answer).
'class'+'struggle'='CLASS STRUGGLE'
Can you help me to learn more?
(Another definition for class struggle that I've seen is " Conflict between workers and the ruling class".)