Bad Best Friend by Rachel Vail

Niki Ames can't wait to start eighth grade, that all-important year before high school. She and her best friend Ava have shared so many plans for the coming year. But then the unthinkable happens: at gym class pair-up, Ava chooses someone else to be her partner. Niki is devastated. It's clear that Ava wants to be part of the popular group, leaving Niki behind. Niki has to decide who her real friends should be, where her real interests lie. Meanwhile, life at home is complicated. Niki's nine-year-old brother Danny continues to act out more and more publicly. Their mother refuses to admit that Danny is somewhere on the autism spectrum, but it's clear he needs help. Niki doesn't want to be like her brother, to be labeled as different. She just wants to be popular! Is she a bad sister and a bad best friend?