In this presentation discussed in this brief abstracted report, the author presents about an ongoing partnership with the Philadelphia School District (PSD) to implement and research the Ongoing Assessment Project (OGAP). OGAP is a systematic, intentional and iterative formative assessment system grounded in the research on how students learn mathematics. The program is being implemented and studied as a mixed method randomized control trial of OGAP impacts in grades 3-5 in Philadelphia area schools. In the spring of 2014, CPRE recruited 60 schools (including charters) in the Philadelphia area to participate in the research study of OGAP. These schools were randomly assigned to treatment and control groups, stratified by charter school and district. The formal research study of OGAP is designed to address the following five central research questions, which are broken down into three implementation questions and two impact questions: Implementation questions include: (1) How do teachers understand the OGAP formative assessment process and use it in their daily practice?; (2) Is the frequency and sophistication of teachers' use of OGAP associated with greater increases in mathematical knowledge for teaching or ability to interpret evidence in student work?; and (3) Is the frequency and sophistication of teachers' use of OGAP associated with greater student learning? Impact questions are as follows: (4) Does teachers' use of OGAP increase mathematical knowledge for teaching and ability to interpret evidence in student work? What moderating factors affect this relationship?; and (5) Does teachers' use of OGAP significantly improve student performance on both proximal and distal student outcome measures? What mediating and moderating factors affect this relationship? The presentation includes a brief description of the study and year one experimental impacts on teachers and students.