Question

why did mrs keesing call anne an incorrigible chatterbox​

Answer 1

Mrs. Kessing called Anne an incorrigible chatterbox because she was annoyed about how much she talked in the class. She had told her many times not to talk in the class, still Anne had to talk. In order to stop her from chattering he gave her an assignment to write an essay on ‘A Chatterbox’.  

When Anne had handed in the essay, Mrs. Kessing enjoyed it and appreciated the sense of humor in it.  However, when the class started again, Anne began talking again. To punish her he gave her another essay to write about ‘An Incorrigible Chatterbox’.

This is how she got this name.

Answer 2

He called her an ‘incorrigible chatterbox’ because of her habit of talking in the class, which annoyed him a lot.