Go wrong, note, having only two-thirds basic education (3)
I believe the answer is:
err
'go wrong' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for err that I've seen before include "Drop a clanger" , "Leave the straight and narrow" , "Blunder" , "Slip up" , "Deviate" .)