Part of educational foundation improperly agreed to alter mark (7)
I believe the answer is:
regrade
'alter mark' is the definition.
'part of educational foundation improperly agreed' is the wordplay.
'part of educational foundation' becomes 'r' (one of the 3 R's - reading, writing and arithmetic).
'improperly' is an anagram indicator (I've seen this in other clues).
'agreed' with letters rearranged gives 'egrade'.
'r'+'egrade'='REGRADE'
'to' acts as a link.
(Other definitions for regrade that I've seen before include "Alter rating" , "Give new status" , "Rank again" .)