This study examines the differential effect of two types of written Corrective feedback (CF) and the extent to which language analytic ability mediates the effects of CF on the acquisition of articles by adult intermediate ESL learners of various L1 backgrounds (N = 91). Three groups were formed: a direct-only correction group, a direct metalinguistic correction group, and a control group. The study found that both treatment groups performed much better than the control group on the immediate posttests, but the direct metalinguistic group performed better than the direct-only correction group in the delayed posttests. It also found a significantly positive association between students' gains and their aptitude for language analysis. Moreover, language analytic ability was more strongly related to acquisition in the direct metalinguistic group than in the direct-only group. The results showed that written CF targeting a single linguistic feature improved learners' accuracy, especially when metalinguistic feedback was provided and the learners had high language analytic ability.