For decades, higher education institutions have undertaken comprehensive and systematic efforts to explore, document, and improve the assessment of student learning outcomes, as well as improving learning itself. However, many of these assessment practices have been designed for full-time traditional students, even as the number of non-traditional students enrolled in higher education continues to grow. One group of these non-traditional students remains particularly invisible on their campuses, in their classrooms, and in assessment practices: part-time students. Part-time students, defined by the U.S. Department of Education's Integrated Postsecondary Education Data System (IPEDS), are students who are not full-time (USDOE, n.d.). This definition inherently defines full-time students as the default assumption, and part-time students as the aberration -- even though nationally speaking, part-time students currently (and historically) make up somewhere around 35-40% of all higher education enrollments (De Brey et al., 2021). The purpose of this study was to focus on part-time students and the student learning outcomes assessment process; specifically, to explore whether assessment practitioners at different institutions were doing anything in particular to measure the learning of part-time students, and to explore with part-time students themselves how they thought about their own learning, how they compared themselves to full-time students, and how they understood assessment practices at their institution. A qualitative phenomenological approach was used to fully explore the richness of the lived experiences of these assessment practitioners and part-time students. Four practitioners and three students participated in semi-structured interviews, which generated more than 11 hours of interview data. These data were coded and analyzed into broad qualitative themes that attempted to capture the full range and depth of these experiences with part-time student learning outcomes assessment. The results raise interesting questions about the nature of part-time learning and how we capture it in assessment practices. The discussion includes some brief recommendations for assessment practitioners. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]