[Grammar] how do I know that the word 'all' is a noun in the phrase?

[learning54]

Hi teachers,
In relation to this question, 'How much of their schoolwork do the children do at home?' This is the correct answer according to a text, 'All of it.'
A teacher told me that 'all' in that answer is a noun.

I know that after and adjective 'all' is always a noun like in the following:
I didn't give it my all.
He puts his all in every game.

My question is, how do I know that the word 'all' is a noun in that phrase? What tells me that it is a noun. How can I easily recognize when 'all' is a noun?

Thanks in advance.

 

[5jj]

'How much of their schoolwork do the children do at home?' This is the correct answer according to a text, 'All of it.'
A teacher told me that 'all' in that answer is a noun.[...]My question is, how do I know that the word 'all' is a noun in that phrase? What tells me that it is a noun. How can I easily recognize when 'all' is a noun?

That teacher is wrong, in my opinion. I think that 'all' is functioning as a pronoun there.

 

[learning54]

That teacher is wrong, in my opinion. I think that 'all' is functioning as a pronoun there.

Hi 5jj,
Thank you for your reply.
If it is functioning as a pronoun, it should substitute ...?

 

[learning54]

With personal pronouns, we use 'all of' + object form, don't we?
In the given answer, 'all of it', 'it' substitudes 'their homework', doesn't it?