For many people, the word "summer" evokes easier days, a time when life slows down. So does the term "summer break," a time parents, teachers, and students alike value as a well-deserved respite from the labor of the school year. Unfortunately, a growing body of evidence shows that summer is far from a time to recharge for many families. Instead, it's a time of loss and lack, a time of struggle and stress. With half of all public school children today living in low-income households, the reality is that summer is actually no vacation at all. The truth is, public schools are a critical lifeline for low-income students and families. When they are open, students of different income levels--rich, poor, and middle class--achieve at roughly the same rate. When they are closed, achievement gaps widen and a variety of academic, health, and social-emotional outcomes decline. So why are schools closed in the summer? This article provides a brief history of the summer break, describes recent research on and advocacy for summer learning, and examines why, despite growing understanding of the issue and support for summer learning, it is still not a priority.