The purpose of this study is to investigate the effects of two implicit input enhancement methods on the learning and retention of four grammar forms: the present continuous, the past tense form of the verb be, the past tense form of general verbs, and the there construction. Seventy-eight students in a Korean middle school were divided into an input flood group, a textual enhancement group, and a control group. The participants were also divided into high- and low-proficiency learners. The results show that the three methods were generally effective in the students’ learning and retention of the grammar forms. The textual enhancement group, however, exhibited the greatest improvement in both the learning and retention of the grammar forms. In relation to the proficiency levels, the low proficiency group demonstrated more gain than the high proficiency group. The findings of this study suggest that different grammar forms require different instruction methods. It is also suggested that multifarious grammar instruction methods be developed to cater to the individual differences that classroom leaners exhibit.