Could 10 min of gratitude per week have the potential to change the trajectories of young students' lives? With over 1,000 ninth- and tenth-grade students, we tested whether a simple 4-week classroom-based gratitude intervention would prompt increases in well-being and motivate students to become better people and attain better grades. Over the course of 1 month, students were assigned to spend 10 min each week writing gratitude letters to their parents, teachers, coaches, or friends and completing additional gratitude-related reflection activities or to try to become more organized each week by listing their daily activities and reflecting on the obstacles and benefits (control). Importantly, relative to controls, students in the gratitude conditions reported greater LS and motivation to improve themselves and maintained these levels throughout the semester. This sustained self-improvement motivation and LS were partially mediated by increases in feelings of connectedness, elevation, and indebtedness. Interestingly, negative affect partially mediated the effect of gratitude on LS, but not on improvement motivation. No group differences emerged in academic performance over time. This study provides evidence that expressing gratitude and reflecting on their benefactors' actions may help keep high school students motivated and satisfied with their lives over the course of a semester. (PsycInfo Database Record (c) 2020 APA, all rights reserved).