Amazing quality of blackboards (10)
I believe the answer is:
remarkable
'amazing' is the definition.
(thesaurus)
'quality of blackboards' is the wordplay.
I cannot really understand how this works, but
'quality' could be 'mark' (mark is a kind of quality) and 'mark' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for remarkable that I've seen before include "Noteworthy" , "Striking" , "unusual" , "surprising?" , "A wrongly-graded exam paper" .)