Crossword Genius

Enthusiastic volunteer having to improve before grammar lesson? (2-6)

Ross

I believe the answer is:

do-gooder

I'm a little stuck... Click here to teach me more about this clue!

'enthusiastic volunteer' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see a link between them that I don't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

I've seen this clue in The Times.
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