The United States' National Institute for Literacy's (NIFL) review of adult literacy instruction research recommended adult education (AE) programs assess underlying reading abilities in order to plan appropriate instruction for low-literacy learners. This study developed adult reading ability groups using measures from power tests and speeded tests of phonemic decoding, word recognition, fluency, and comprehension. A multiple cluster analysis of these reading ability scores from 295 low-literacy AE participants yielded seven reading ability groups. These groups are described in terms of instructional needs relevant to an instructor's planning and activities.