In secondary education? Rest and eat before start of exam (7)
I believe the answer is:
teenage
'in' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for teenage that I've seen before include "13 to 19 years old" , "Thirteen to nineteen" , "Suitable for years 13-19" , "Gee, neat (anag)" , "Tea gene (anag.)" .)