Math experts developed Formative Assessment Lessons that teachers can incorporate throughout the year's curriculum. Both tools target the "instructional core." A study by Research for Action (RFA) examining the first year of piloting the Literacy Design Collaborative (LDC) and Math Design Collaborative (MDC) tools (2010-11) found evidence of initial success in tool use indicated by teachers' perceptions that the tools positively influenced teacher practice. In the second year of the Initiative (2011-12), tool use grew within and across sites. The focus of the research has expanded accordingly to include an analysis of how the tools are being introduced to additional classrooms, schools and districts, and what strategies are most effective in sustaining and strengthening tool use. This brief focuses on efforts to scale up and sustain broader use of the tools. It begins with an introduction in which "scale-up and sustainability" is defined, providing the framework for this brief. The introduction also provides detail on the extent to which use of the tools has grown within study sites, both in terms of additional teachers/schools/districts/networks, and in terms of the greater integration of the tools into teachers' practice. In addition, the authors provide a review of the theory of action driving the LDC/MDC Initiative, highlighting the underlying conditions necessary for robust implementation to occur. The second section of the brief presents findings on the extent to which the supporting conditions necessary for robust LDC/MDC tool implementation--alignment, leadership and professional learning opportunities--are in evidence at the various study sites. The final section of the brief offers suggestions for supporting enhanced and expanded LDC/MDC tool implementation. Findings in this brief draw on observations of teachers and professional development providers, interview data from tools developers and professional development providers, and interview and survey data from teachers, school administrators, district/regional and network leadership, and state-level policymakers/partners. (Contains 28 figures and 4 footnotes.)