Understood to make the grade (8)
'understood' is the definition.
('gather' can be a synonym of 'understand')
'make the grade' is the wordplay.
'make' is an anagram indicator.
'thegrade' is an anagram of 'GATHERED'.
'to' is the link.
(Other definitions for gathered that I've seen before include "Surmised", "Concluded from evidence", "Gleaned", "Collected - inferred", "Understood".)