This thesis investigates adult native English speakers' acquisition of Italian (L2) grammar via enrollment in college courses. Predictions are derived from the Competition Model (Bates & MacWhinney, 1982; 1987; 1989) according to which subject-verb agreement (SVA) is a vertical cue, reflecting a correlation between word form and meaning (e.g., subject noun - agent role). Noun-adjective agreement (NAA) is a horizontal cue, reflecting a correlation between word forms only. SVA should be acquired by L2 learners sooner than NAA because of its vertical mapping. However, constructions in which SVA has an irregular mapping should be difficult to acquire. For example, the Italian verb piacere (to like) has a mapping of grammatical-thematic roles that is irregular in both Italian and English (i.e., subject-theme, object-experiencer). The predictions were tested with a grammaticality judgment task that was administered in the middle and end of a semester to beginner and advanced learners. The task measured sensitivity to agreement violations in spoken sentences representing the three conditions (SVA, irregular-SVA, and NAA). General factors that may affect learning, such as working memory capacity, motivation to learn, knowledge of other languages, etc, were also assessed. Both groups had higher A' scores in the SVA condition than in the other two conditions. The implications of these results for the Competition Model as well as effects of other general learning factors are discussed.