This study investigated whether recasts provided during communicative interaction may improve Korean EFL learners' accuracy with regard to regular and irregular English past tense forms, and whether individual differences in working memory capacity may intervene in the effects of recasts. To this end, forty-two Korean university students were placed into either the recast or the control group, and took the pretest and two types of working memory tests: phonological short-term and verbal. The learners participated in one-on-one conversational interactions with the researcher in three two-way communicative tasks one at a time on a weekly basis. Only the treatment group received explicit recasts on their past tense errors while the control group received no feedback of any kind. Finally, they took the posttest and completed the exit questionnaire. Results showed that recasts were beneficial for raising the learners' accuracy level of English past tense forms, both regular and irregular, though the effects were much larger for the irregular forms. The improvements were not significantly correlated with neither of the working memory measures. Explicit and intensive recasting alone was sufficient in improving EFL learners' English past tense accuracy in this one-on-one communicative interaction setting.