The kids in P.S. 8 are anxious for summer vacation to begin because, well, summer vacation is awesome.
Shirley's started to adapt to school—even saying the Pledge of Allegiance, albeit incorrectly (hence the chapter's title).
She asks Mrs. Rappaport why the other kids call her Jackie Robinson, and Mabel explains it's because Shirley's a good baseball player. The Brooklyn Dodgers are the best team out there.
Mrs. R proceeds to tell the class why Jackie is so important to America. Basically, he created a new future for himself before by breaking race barriers in baseball.
Only in America, she says, can anyone pursue his or her own happiness to the fullest extent, no matter how rich they are or where they're from. Because of this, every one of the kids in her classroom can, and should, make their country a better place.
Jackie represents this American Dream; he took on injustice and defeated it to make his own dream come true. This is one dream Shirley can get behind.