Building on Sheen's (2007) study of the effects of written corrective feedback (CF) on the acquisition of English articles, this article investigated whether direct focused CF, direct unfocused CF and writing practice alone produced differential effects on the accurate use of grammatical forms by adult ESL learners. Using six intact adult ESL intermediate classes totaling 80 students, four groups were formed: Focused Written CF group (FG, n = 22), Unfocused Written CF group (UG, n = 23), Writing Practice Group (WPG, n = 16) and Control Group (CG, n = 19). A series of ANOVAs with post-hoc comparisons indicated that all three experimental groups (FG, UG and WPG) gained in grammatical accuracy over time in all the posttests. This suggested that doing writing tasks is of value by itself. The FG achieved the highest accuracy gain scores for both articles and the other four grammatical structures (i.e., copular "be", regular past tense, irregular past tense and preposition), followed by, in order, the WPG, UG and CG. Overall, these results suggested that unfocused CF is of limited pedagogical value whereas focused CF can contribute to grammatical accuracy in L2 writing. (Contains 6 tables.)