Tense, you say, when under instruction (6)
I believe the answer is:
taught
'tense you say when under instruction' is the definition.
I can't judge whether this defines the answer.
'tense you say' is the wordplay.
'tense' becomes 'taut' (similar in meaning).
'you say' indicates a 'sounds like' (homophone) clue.
'taut' is a homophone of 'TAUGHT'.
Can you help me to learn more?
(Other definitions for taught that I've seen before include "Tutored" , "given a lesson" , "Educated" , "Gave instruction" , "Instructed, schooled" .)