Schoolchildren are not out to sweat at it (8)

I believe the answer is:

homework

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'it' is the definition.
The definition suggests a singular noun which matches the answer.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for homework that I've seen before include "DIY" , "It's done outside school hours" , "Preparation before lesson" , "School prep" , "something to do after school" .)

I've seen this clue in the Evening Standard.

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