This dissertation is a first look at English-speaking children’s acquisition of the syntax of the partitive. It presents four experiments that contrast three types of structures and examines how they interact with adjectival modification: the partitive, the pseudopartitive and complex nouns with prepositional adjuncts. The experimentation investigates whether children recognize that the Determiner Phrase (DP) in the partitive is a barrier to adjectival modification. The partitive is contrasted with the pseudopartitive –a minimal pair structure that lacks an internal DP. The data shows that children under the age of six do not distinguish between the partitive and the pseudopartitive. They allow adjectives preceding the partitive to modify the second noun; this is standardly considered licit for the pseudopartitive structure, but not the partitive. This result is evidence that children are under-representing the syntax of the partitive and of DP. Syntactic representations of minimal DP and minimal partitive structures are suggested and it is argued that these structures may persist as an option in the adult grammar. Chapter 2 discusses multiple layers in DP, DP’s status as a barrier/phase and how children acquire its syntax (Abney 1987, Cinque 1994, de Villiers & Roeper 1995, Kupisch 2006, Bošković 2008). This chapter also includes evidence for an underrepresented DP in the grammar of some adult English speakers (Schafer & de Villiers 2000, Carlson et al 2006). Chapter 3 presents background literature on the syntax of the partitive (Jackendoff 1977, Hoeksema 1996), introduces the pseudopartitive structure (Selkirk 1977, Stickney 2004 and Alexiadou, Haegeman & Stavrou 2007) and presents acquisition hypotheses. Chapters 4 & 5 present a pilot experiment and three picture choice tasks. The experimental data shows that children and a subset of adults do not distinguish between partitive and pseudopartitive and yet they maintain a clear distinction between pseudopartitive and other similar complex nouns. Chapter 6 presents two syntactic analyses of the data. One uses a split-DP structure (Zamparelli 2000, Laenzlinger 2000) to explain the lack of barrier in children’s partitives. The other suggests a reduced partitive structure (Rutkowski 2007). Both analyses require a reanalysis of the features of DP in children’s partitives.