This experimental study tests the Interface Hypothesis by looking into processes at the syntax-discourse interface, teasing apart acquisition of syntactic, semantic and discourse knowledge. Adopting Lopez's (2009) pragmatic features [[plus or minus]a(naphor)] and [[plus or minus]c(ontrast)], which in combination account for the constructions of dislocation and fronting, we tested clitic left dislocation and fronted focus in the comprehension of English native speakers learning Spanish. Furthermore, we tested knowledge of an additional semantic property: the relationship between the discourse anaphor and the antecedent in clitic left dislocation (CLLD). This relationship is free: it can be subset, superset, part/whole. Syntactic knowledge of clitics was a condition for inclusion in the main test. Our findings indicate that all learners are sensitive to the semantic constraints. While the near-native speakers display native-like discourse knowledge, the advanced speakers demonstrated some discourse knowledge, and intermediate learners did not display any discourse knowledge. The findings support as well as challenge the Interface Hypothesis. (Contains 13 notes, 4 figures and 8 tables.)