Across the long arc of adolescent development, researchers have long suspected that rest shapes more than mood—and now, a large-scale study from the University of California, Davis confirms it with unusual clarity. Analyzing data from more than 6,000 young people aged 10 to 13, scientists found that sleep quality surpasses screen time, diet, and physical activity as the dominant lifestyle factor connecting mental health to academic and social outcomes. For teenagers already navigating anxiety or depression, poor sleep acts as the mechanism that transforms inner struggle into visible failure—in