It's Not the End of the World by Judy Blume

It’s Not the End of the World by Judy Blume 1972
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Middle child Karen is looking forward to starting 6th grade in the fall. Her home life changes all that. Her parents are getting divorced after 16 years of marriage. When Karen tries to seek information from 14-year old brother Jeff, he doesn’t want to talk to her or anyone. 6-year old Amy has to sleep in Karen’s room every night because she is scared everyone is going to leave like Daddy did.

Karen meets and becomes friends with her Dad’s downstairs neighbor Val, whose parents are divorced and her mom is dating (but not dating her dad). Seventh-grade Val tells Karen about a book to help explain divorce to kids. Karen is constantly worried her mom or dad will meet someone else and marry and then they won’t get back together. She is constantly thinking of ways to get them together-get sick, bring Dad inside the house to see her project. Mom gets a job and takes classes in typing and shorthand. She explores the idea of getting her college degree because she only went to college one year before getting married. Jeff feels like it is his fault for Mom not finishing college and runs away. When he returns he advises Karen not to ever run away because it is difficult on your own. Eventually Karen realizes her mom and dad only fight when they are together and they are better apart, accepting in her heart and mind that they will divorce and not ever get back together.