Since the passage of the No Child Left Behind Act (2001), districts, schools, and educators are pressured to collect, analyze and report data annually regarding student performance. If high-stakes assessments are to be useful tools for educators in their classrooms, the data need to be applicable in conveying meaningful instructional information that supports not only school-wide but also individual student improvement. The identification of student difficulty depends on valid assessment measures and effective educators who are competent of recognizing the value of using data to drive instructional decisions. In-class professional development opportunities made available through literacy coaches can provide teachers with assistance in understanding the significance of using assessments to support literacy instruction. This study emphasizes the role of schools in utilizing data and ongoing classroom-based professional development to drive instruction that enables kindergartners to make progress in literacy. The objective of this study is to determine the measurable effects in literacy as a result of systematic and explicit data-driven instruction derived from classroom-based assessments and collaborative teaching among kindergarten learners. To assess the levels of student achievement, the study utilizes a mixed-method design to clarify and illustrate both quantitative and qualitative information. Quantitative evidence of student achievement is demonstrated through phonemic awareness assessment data presented through ANOVA and SPSS comparisons. Additionally, qualitative research investigates classroom teachers' perceptions regarding coaching and collaboration. Interview results are presented to identify specific outcomes of the year-long study. The development of the teachers' professional experience and collaboration, as well as their understanding of assessment and data-based instructional decisions are described. Findings for this study indicate that student achievement scores were improved as a result of data-driven instructional decisions derived from a combination of formative and summative assessments. Additional effects in early literacy progress were demonstrated through classroom teachers working collaboratively with a literacy coach to assist in the process of professional learning, according to the results of this study. Recommendations focus on the importance of promoting professional development opportunities for classroom teachers. Assessments to support instructional decisions and effective early literacy instruction necessitate continuous learning experiences on behalf of both educators and students alike. [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.]