Organizations have often used data and instituted accountability practices to improve performance by optimizing individual and organizational behavior. While research has focused on the impact of quantification on behavior, the increasingly important aspects of wellbeing and motivation are often ignored. However, the dynamics and politics of quantification can have important consequences to internal personal processes, over and beyond external observable actions. Using the case of US education that has long relied on accountability policies, we find that attendance in schools with test-based accountability predicted lower student self-efficacy, i.e., decreased task motivation and resilience as well as increased fear of failure—salient for low-income, urban, and public schools. These associations, however, did not spill over to social and life satisfaction dimensions of wellbeing. Taken together, these suggest the irony of accountability, where data used to induce performance may unintentionally reduce people’s motivation to perform—particularly consequential in disadvantaged contexts. This paper attempts to contribute to a broader theorization of quantification, affecting not only external behaviors and interpersonal relations but also internal personal dispositions. Finally, the paper also provides implications for the study of wellbeing, organizations, and education policy.