Adult literacy learners are characterized by their diversity, both in terms of educational histories and cognitive skill sets. Accounting for the specific strengths and weaknesses of each learner is vital to the assessment of literacy gains and optimization of educational systems. We examined pre- and post-difference scores on a component reading skills assessment battery collected before and after an instructional program that included an adult comprehension-focused intelligent tutoring system. By characterizing learners during instruction, we examined differential gains in foundational reading skills. Most learners made gains in reading skills above the word recognition and decoding level; readers who were classified as "conscientious" (who performed slowly but accurately) tended to make the most substantial gains. We conclude that this hybrid instructional program may be an effective educational environment for adult literacy and describe how characterizing learners via integrating assessments into adaptive instructional practice may improve efficiency and effectiveness. [For the corresponding grantee submission, see ED628313.]