Little is known about which educational activities are most associated with incarcerated adults' literacy and numeracy skills. The present study examines whether informal engagement in reading, writing, and numeracy activities (e.g., reading newspapers or using calculators) is associated with incarcerated adults' literacy and numeracy skills. Using the 2014 Program for the International Assessment of Adult Competencies (PIAAC)--U.S. Prison Study, numeracy/literacy skills were predicted from engagement in reading, writing, and numeracy activities. Literacy skills were higher among incarcerated persons who engaged in an increasing amount of writing activities along with those who completed postsecondary coursework in prison. Literacy skills and numeracy skills were not significantly associated with engagement in reading activities and numeracy activities, respectively. Findings highlight promising strategies for restructuring prison education.