As others answering your question have mentioned, the phrase "main events" is ambiguous and will vary from reader to reader. What I consider to be the main events may be different from what you consider the main events to be, and chances are that if you discussed as many as 20 points in an essay, your points would be rather diluted.
The first "incident" to discuss would be Maleeka Madison being teased about the color of her skin. You'd definitely mention that a new teacher, Miss Saunders, arrived at McClenton Middle School. Miss Saunders is a particularly significant character because he has a facial skin disorder, and in a strange way, this makes Maleeka feel better abut herself because there's someone else who's skin isn't "normal."
Over time, Miss Saunders notices that Maleeka is a good writer, which allows Maleeka to build some newly-won self confidence. In my opinion, another important moment in this great story is when Maleeka realizes that she has been judging Miss Saunders cruelly, in the exact same manner in which her classmates have been judging her.
Another important incident is Maleeka and her classmate, Char, coming to a twisted agreement in which, in exchange for Char being superficially friendly to her and lending her clothes, Maleeka will do Char's homework for her.
This great novel for young adults is filled with significant events, life lessons, and reminders of the fact that everyone's words and actions have an impact on other people.