The COVID-19 pandemic prompted an abrupt adoption of online learning worldwide challenging students' scholastic engagement and their ability to self-regulate their learning. Under these unexpected conditions, adaptability (one's capacity to adjust thoughts, behaviors, and emotions in new and uncertain situations) might have sustained students to maintain high engagement and find new learning solutions. Students with high adaptability might also interpret COVID-19-related novelty as an opportunity and show higher posttraumatic growth levels. A longitudinal path analysis showed that in a sample of 435 Italian students (11-18 years old), adaptability at Time 1 positively related to engagement, self-regulated learning, and posttraumatic growth at the end of the school year, indirectly favoring academic achievement, through the mediation of engagement and self-regulated learning. These findings highlight the unique role that adaptability could play in supporting students in unexpected and stressful situations. Fostering students' adaptability could therefore have beneficial effects on their personal growth and academic success.