"I’m upset over nothing in basic education," one reflects (6)
I believe the answer is:
Here is my best explanation:
'one reflects' is the definition.
'i'm upset over nothing in basic education' is the wordplay.
'upset' says the letters should be written in reverse.
'over' is an insertion indicator.
'nothing in' becomes 'o' (I've seen this in other clues).
'basic education' becomes 'rrr' (the three R's - reading, writing and arithmetic).
'im' reversed gives 'mi'.
'o' inserted within 'rrr' is 'rror'.
(Other definitions for mirror that I've seen before include "Reflective surface", "Paper", "Glass for reflection", "What reflects", "double", "Reflector", "Glass - paper", "Image reflector", "Something studied constantly by the vain?" and "copy of > tabloid".)