Given the sentences:

The Gryffindor common room was very noisy that evening. Harry, Ron, and Hermione sat together next to a window. Hermione was checking Harry and Ron's Charms homework for them. She would never let them copy ("How will you learn?"), but by asking her to read it through, they got the right answers anyway.

What does the yellow ‘it’ indicate?
I think it refers to "Harry and Ron's Charms homework",

where can you find it