What is the plot of Blubber by Judy Blume?

In Blubber, Jill Brenner tells the reader about how she & everyone in her fifth grade class gang up on a fellow classmate, named Linda Fisher. Linda Fisher is overweight, and when she chose to do her science report on the Whale, is immediately nicknamed by everyone as 'Blubber.'

From that point onward, the kids constantly harass & degrade Linda, making her cry.

Jill eventually finds out what it is like to be bullied, when she breaks from the crowd, and they all turn on her.