One of the great puzzles of language acquisition has been described as poverty of the stimulus: how are complex aspects of language acquired when they appear to be rare or even non-occurring in the input that a learner receives and comprehends? This article presents an emergentist solution to one aspect of this puzzle (involving relative clauses) by examining the longitudinal development of meaningful discourse produced by Ana, a 12-year-old Spanish learner of English. Relative clause constructions are considered in terms of learnable, non-abstract linguistic analyses (lexicalist signs and constructions; dependencies), informed by emergentist syntax (O'Grady 2005), analyses within Head-driven Phrase Structure Grammar (Sag 1997), and a comprehensive corpus grammar (Biber et al. 1999). The data show that complex aspects of language gradually emerged from item-based and compositional learning processes that interacted with the learner's environment, including input frequency and the functional purposes for which language is used. Item-based, sign-based, and compositional analyses of constructions are valuable for syllabus design (for synthetic syllabi) and for the evaluation of language proficiency (i.e. testing and measurement).