Shows given low grades by old people (7)
I believe the answer is:
depicts
'shows' is the definition.
('depict' can be a synonym of 'show')
'low grades by old people' is the wordplay.
'low grades' becomes 'de' (D and E are low academic grades).
'by' says to put letters next to each other.
'old people' becomes 'picts' (I am not sure about this - if you are sure you should believe this answer much more).
'de'+'picts'='DEPICTS'
'given' is the link.
Can you help me to learn more?
(Other definitions for depicts that I've seen before include "Paints or draws something" , "Describes or shows as picture" , "outlines" .)