Childhood disadvantage is associated with psychological distress throughout the lifespan. Poor children are alleged to give up more often than their more privileged peers when facing challenges. Yet little research has examined the role of task persistence in poverty and mental health. We test whether poverty-related deficits in persistence contribute to the well-documented link between childhood disadvantage and mental health. We used growth curve modeling to analyze three waves (ages 9, 13, and 17) of data assessing the trajectories of persistence on challenging tasks and mental health. Childhood poverty is the proportion of time participants lived in poverty from birth to age 9. We found that individuals experiencing more poverty in early childhood demonstrate less persistence and deteriorated mental health from ages 9 to 17. As expected, task persistence accounts for a portion of the robust childhood poverty--worsening mental health association. Clinical research on childhood disadvantage is in the early stages of unpacking underlying reasons why childhood poverty is bad for psychological well-being throughout life, revealing potential points of intervention.