In grammar schools, it's astronomical! (4)
I believe the answer is:
mars
'in grammar schools it's astronomical' is the definition.
I can't judge whether this defines the answer.
'in grammar schools it's astronomical' is the wordplay.
'in' indicates the answer is hidden within the clue.
'MARS' can be found hidden inside 'grammar schools astronomical'.
Can you help me to learn more?
(Other definitions for mars that I've seen before include "Damages - planet" , "Spoils - planet" , "RS [RED STAR] (not technically)" , "Fourth planet from the Sun" , "Injures - god of war" .)