This evaluation report addresses the implementation, utility, and feasibility of SimScientists' simulation-based assessments for middle school science classrooms, with particular attention to the use of accommodations available in the program. Data were collected from a convenience sample of five schools and eight teachers across three states participating in a larger pilot of SimScientists. During site visits, CRESST researchers conducted classroom observations and teacher interviews addressing the major components of the SimScientists program in two topics: (1) Ecosystem and (2) Force and Motion. SimScientists components included embedded, formative assessments; reflection activities designed to deepen student understanding of key ideas and processes; and benchmark assessments to gauge student learning at the end of the unit. Site visit findings were confirmed using teacher survey results from the larger pilot on teachers' use and satisfaction. Embedded and Benchmark Assessments are appended. (Contains 17 figures and 23 tables.)