Teach girl strangely lacking in energy (9)
I believe the answer is:
lethargic
'lacking in energy' is the definition.
(I've seen this before)
'teach girl strangely' is the wordplay.
'strangely' is an anagram indicator.
'teach'+'girl'='teachgirl'
'teachgirl' with letters rearranged gives 'LETHARGIC'.
(Other definitions for lethargic that I've seen before include "Enervated" , "without energy" , "Sluggish and apathetic" , "lack of energy" , "languid" .)