Answer:
lay emphasis on the things the speaker strongly wants the readers to know.
Step-by-step explanation:
The effect of a phrase that repeats, such as "Not Mine, Not Mine, Not Mine" is that it lay emphasis on the things the speaker strongly wants the readers to know. In the story, it places emphasis on how much Rachel wanted her teacher and the other students to know that the coat did not belong to her.
Since Rachel wanted to become a hundred and two years old person instead of eleven because she thought that maybe it would help her make people listen to her, the use of such type of sentence in the story develop the idea why Rachel wanted to become a very old person.
Though she continously repeated "Not mine, Not mine, Not mine", she knew that no one would listen to or believe her because she was just a kid.