The Common Core State Standards (CCSS) were adopted by most states by 2010. Yet, many teachers still lack confidence in their ability to integrate these standards into their classroom instruction and this uncertainty undermines their effectiveness. This article presents findings from a study of a fourth grade literacy curriculum informed by the CCSS. The study mobilized the Vygotskian notion of mediation as it applies in a literacy learning context and addresses the following research questions: (a) What were fourth grade student English language arts achievement levels and beliefs about literacy prior to and following the implementation of a CCSS-based curriculum? (b) What was the collaborating teacher's response to participating in the implementation project? and (c) What roles did mediating tools play within this literacy learning system? Several types of data were collected: unit assessments from the core curriculum; scaled scores from the state standards test; Informal Reading Inventory and interview responses from six focal students; and teacher interview responses. Analysis demonstrated (a) gains by all students, particularly those who struggled, on all assessment measures, (b) increased metacognitive awareness and positive changes in beliefs about reading on the part of focal students, (c) the teacher's growing confidence in and commitment to the new curriculum, and (d) a growing use of mediational tools by students. These findings support the argument that a structured CCSS curriculum, adapted by classroom teachers, can serve as an important tool serving to mediate the space between students and literacy achievement.