The meaning of “from that of”

Question

I came across the following sentence on a website:

Deaf children's emotional development differs from that of hearing children.

I am guessing that the sentence simply mean that deaf children's emotional development differs from hearing children. But I may not be aware that the phrase "from that of" could have changed the meaning of the sentence.

How does the phrase "from that of" add meaning to the sentence?

What does "that" refer to in the sentence?

Answer 1

That is just a placeholder. Don't worry about whole phrase "from that of", just look at its individual parts:

Deaf children's emotional development differs from that of hearing children.

is the same as

Deaf children's emotional development differs from [the emotional development] of hearing children.

or, to put it another way:

Deaf children's emotional development differs from hearing children['s emotional development].

Answer 2

From that of is not a set phrase; the sentence should be parsed as

• Deaf children's emotional development
• differs from
• that — a pronoun referring to [deaf children's emotional] development
• of hearing children

The sentence could more explicitly be phrased as

The emotional development of deaf children differs from the emotional development of hearing children.

Without phrasing in this manner, differs from becomes illogical, as it would instead express

[...] Development differs from hearing children.

Answer 3

'that of' emphasizes that the topic is emotional development rather than children.