The ideas students have about what causes math failure are known to impact motivation. This paper throws light on how attributions of failure are negotiated during math tutoring, between 4th/5th graders and volunteer tutors, at a non-profit STEM-based after-school program. The study employs methods of interaction analysis on a small number of cases to qualitatively document how tutor-student dyads co-construct stories about failure. I argue that responses to failure involve constructing obstacles, blaming causes of obstacles, and intervening to resolve obstacles, which take place as part of public practice. By understanding the interactional mechanics of failure, the study can inform discourse-level interventions in the future.