From Sarah Jane Abbott, an associate editor for Paula Wiseman Books and Beach Lane Books/Simon & Schuster, who spoke at Austin’s SCBWI conference:
After the novel has been submitted and accepted (if I remember correctly),
the editor will read, line edit, and check changes on a draft.
They will also send an edit letter with bigger ideas (such as–from other authors’ experiences–delete this part of the storyline, because you have too many characters).
Then, for Ms. Abbott, there will be a long phone call, after which she will wait for the new draft.
Repeat the above steps until the editor is satisfied. (She didn’t say how many times before it wouldn’t happen anymore.)
Then the copy editors read the book and send notes to the author, who once again revises it.
After that, the book is designed and typeset.
Specifically in connection with Beach Lane Books, Ms. Abbott said that the acquiring editor does the progressive rounds. At other houses it may be someone else.