Learning to read marks a critical transition in a child's educational trajectory that has long term consequences. This dissertation analyzes how California's current policies in beginning reading instruction impact two critical conditions for creating opportunity--access to qualified teachers and rigorous academic curriculum--by examining the enactment of a prescriptive core reading program disproportionately targeted at "low-performing" schools. Although prescriptive curricula attempt to ensure achievement, classroom implementation is mediated by teachers exercising professional prerogative. The quality of these mediations may be determined by a teacher's expertise in negotiating the tensions between fidelity of implementation and adaptation to local context. Through classroom observations and teacher interviews, this multi-case study illuminates fundamental issues of teacher quality as they are realized by experienced teachers exercising professional prerogative with prescriptive curriculum in order to be more effective with their students. The findings indicated that instructional decisions and strategies of effective teachers were driven by a clear definition of equity based on a theory of action that included mechanisms for both expanding access and achieving desired outcomes. These theories of action allowed teachers to exercise professional prerogative to utilize content and pedagogy both within and beyond the prescribed curriculum. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]