The purpose of this holistic case study with a mixed methods approach was two-fold: first, to investigate the extent to which elementary teachers in the BTSD sustained the use of formative assessment reform to regulate instruction, and second, to explore the factors that promoted fidelity to formative assessment reform. Although this study examined the experience of elementary teachers in one school district with a specific reform initiative, the findings may have implications for teachers in other school districts and organizations which have attempted to implement various reform efforts. The Formative Assessment Practices Questionnaire was used to survey teachers from four elementary buildings in one school district. The researcher designed the instrument to collect quantitative and qualitative data simultaneously. Quantitative and qualitative data analysis revealed that respondents regularly collected, analyzed, and used student-learning data to regulate instruction two and a half years after the implementation of formative assessment by the Bolden Township School District. Quantitative and qualitative data analysis revealed that (a) teacher involvement in collegial learning communities, (b) teachers' perception that formative assessment reform matches personal learning needs, (c) principals' commitment to reform, (d) district-wide leadership team's support of reform, and (e) teacher contact with experts related to the innovation promoted reform to varying degrees. Correlation analysis revealed statistically significant relationships among the independent variables: (a) dedicated time for collegial interaction, (b) district-wide leadership team's support of reform, (c) teacher participation in collegial learning communities, and (d) the match between teachers' instructional theory and formative assessment reform theory, and the dependent variable, the state of formative assessment reform. Three themes emerged from qualitative analysis: (a) the influence of principals' actions on teachers' commitment to reform, (b) the emergence of collegiality, and (c) the apparent disconnect between central administration's and teachers' long-term vision for formative assessment reform. Multiple regression analysis revealed that two independent variables significantly predicted the state of formative assessment reform: dedicated time for collegial interaction and the match between teachers' instructional theory and formative assessment reform theory. Stepwise analysis revealed years of teaching experience significantly predicted the state of formative assessment reform; more experienced teachers were less likely to sustain reform. [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.]