The most common and most likely answer to this crossword clue is the 12 letter word HIERARCHICAL
I've seen this crossword clue in The Guardian
H
I
E
R
A
R
C
H
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C
A
L
Buddy explains!

The straight part
We know that "graded" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case graded = hierarchical.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HIERARCHICAL mean?
HIERARCHICAL adjective- Pertaining to a hierarchy.
- Of or pertaining to an ecclesiastic or priestly order.
- Classified or arranged according to various criteria into successive ranks or grades.