Put former pupil back - result is the power of belief (7,6)
I believe the answer is:
placebo effect
'the power of belief' is the definition.
The definition suggests a singular noun which matches the answer.
'put former pupil back result' is the wordplay.
'put' becomes 'place' (synonyms).
'former pupil back' becomes 'bo' (I can't justify this - if you can you should give a lot more credence to this answer).
'result' becomes 'effect' (synonyms).
'place'+'bo'+'effect'='PLACEBO EFFECT'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for placebo effect that I've seen before include "psychological remedy" , "Inactive drug's result relying on the patient's belief in its worth" , "Psychological action of inert drug" .)