The dissertation project is a study of how childrens' increasingly skillful use of certain language forms ("stance forms") help them to more effectively perform culturally salient social identities in discourse. Although scholars have long claimed that language use helps to position speakers in terms of socially recognizable identities, very little is known about the genesis or formation of these relationships--that is, how language structure and function become entwined with identity during the course of communicative development. My approach uniquely targets a child's developing communicative abilities--rather than, for example, the role of explicit parental socialization--as enabling more skillful mobilizations of identity in discourse. In doing so, I develop a line of language socialization theory that is "constructivist" or neo-Meadian (G. H. Mead) in its focus on the role of the child's emerging discursive abilities in socialization. I take up this question among Aymara-speaking Peruvian boys for whom masculinity (specifically, masculine potency) is a significant dimension of everyday life. Drawing on 18 months of linguistic and ethnographic fieldwork, I use longitudinal evidence to show that the acquisition of Aymara stance forms plays a decisive role in the formation of masculinity during middle childhood. Though masculinity is a constant concern in Aymara boyhood, I pay special attention to a practice in which every move is understood to speak to a boy's masculine identity--the boys-only game of marbles. There are two dimensions to this understanding of masculinity. First, boys--in marbles and elsewhere--must appear tough in the face of bad luck ("qhincha") and adversity. Second, boys must display their expertise over game play and regulate the relatively "tough" behavior of their younger brothers. Taken together, these two components of masculinity--toughness and relative maturity--form an understanding of masculinity (one that I call "masculine potency") that is clearly related to analogous adult understandings of masculinity (specifically, understandings of adult masculine strength or "ch'ama" as evidenced in the political and religious life of the village). In the central chapters of the dissertation, I follow the linguistic and social trajectories of five boys in order to chart out how their increasingly effective use of these two forms allows them to more capably cast themselves as both tough and relatively mature (i.e., as "potent" in a specifically masculine way). As boys come to use animal-oriented interjections in skillful ways, for example, they are increasingly able to cast their marble as subject to the intervention of bad luck ("qhincha") and adversity (thereby casting themselves, implicitly, as tough). As boys come to use manner deictics in skillful ways, they are increasingly able to make claims about the regular, normative ways of playing marbles (i.e., playing it "tough") as a form of informal instruction with their younger brothers. Although these changes are evident to the careful observer, the boys themselves interpret them as meaningful. Boys less skilled in stance were mocked for their unmanly or immature play (as "qachu" or "fags"). More skilled boys evaded these insults. My dissertation, then, offers a case study of the way in which an agent's increasing skillfulness with language (specifically, stance forms) mediates their construction and inhabitance of culturally salient identities. In doing so, it provides an empirical example of an undertheorized strain of language socialization theory--that is, one in which the analytical lens is turned towards a novice's increasing language ability as a powerful mediator of socialization processes (and away from an expert's intervention through routines like, for example, prompting routines). Such an analytic is best captured through a set of metaphors about the way that language serves as a "tool" or "bootstrap" that helps set processes of socialization into motion. It is a logic that, in an ethnographic sense, helps show yet another way in which seemingly natural social facts (e.g., masculinity) are temporally contingent: what might other language-mediated biographical trajectories reveal about the constructedness of social factualities? (Abstract shortened by UMI.) [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]