Second language acquisition research on the immersion context has focused primarily on study abroad, revealing the extent to which that context promotes learners' developing linguistic and intercultural competence. However, little research has examined linguistic development in intensive, domestic immersion contexts. This study investigated the extent to which target language interactions in a seven-week domestic immersion program predicted the acquisition of linguistic features that are not present in the learners' native language or taught in the classroom. In addition, it addressed the way in which learners' affective characteristics may account for variability in linguistic outcomes. Data obtained for 98 participants--including self-reported individual variability questionnaires, language contact surveys, and questionnaires measuring the accuracy of left-headed noun-noun compounds, verb-particle constructions, and resultatives--showed an association between the development of these syntactically complex structures and the amount of interaction with target language speakers in which participants reported engaging. Some participants also reported positive changes in their affective characteristics due to their participation in the intensive domestic immersion program. By emphasizing how language reflects the participants' social environment, this analysis suggests that the contextual properties of a domestic immersion program can support language learners' acquisition of syntactically complex linguistic elements.