This study investigates the effects of task-essential training on offline and online processing of verbal morphology and explores how working memory (WM) modulates the effects of training. We compare a no-training control group to two training groups who completed a multisession task-essential training focused on Spanish verbal inflections related to person–number agreement and tense. Effects of training were evaluated using an offline aural interpretation task and an online self-paced reading (SPR) assessment, administered as a pretest, posttest, and delayed posttest. Results showed that training led to more accurate interpretation of both person-number and tense information in the offline interpretation test. While higher WM was associated generally with greater accuracy, higher WM did not lead to greater gains from training. The SPR results showed that training did not increase sensitivity to subject–verb agreement or adverb–verb tense violations. However, among participants who underwent training, WM enhanced sensitivity under some conditions. These results demonstrate a role for individual differences in WM for offline and online processing, and they suggest that while task-essential training has been shown repeatedly to improve offline processing of target forms, its effects on online processing of redundant verbal morphology are more limited. Implications for L2 learning are discussed.