The present paper provides evidence that children are not different from adults with respect to phrase structure building, a process considered to be highly dependent on feature valuation. Lexical heads are taken from the lexicon with open feature values that are specified in the course of the derivation. Under such a view, linguistic development is mainly restricted to the lexicon, the projection of functional structure following from the stepwise identification and valuation of the features encoded by the morphological markers on lexical items. Based on data from child language, it is argued that language acquisition consists in choosing the particular values that correspond to the target language.