This study focused on using intensive computer-based instruction to improve the learning outcomes of five adult functional illiterates who participated in a literacy class at an adult education center. During training sessions, they practiced 32 training words with three different highlighted sublexical onsets for 15 minutes on a daily basis. Results of the study indicated an increase in reading accuracy and fluency. However, only word specific training effects were found (i.e., transfer effects on untrained words could not be shown). Moreover, when compared to a control group of adults without reading problems, participants read more slowly at every measurement point (pre, post, and follow-up tests). Possible interpretations regarding the lack of transfer effects and the poor reading fluency of functional illiterates will be discussed, as well as implications for the literacy training of individuals in adult basic education.