This paper describes a model for building cognition-and-instruction-based goal trajectories (GT) in the context of a study that examines the validity of curriculum-embedded assessments. The model consists of six design processes and two constraints. The GT is constructed from curriculum-specified learning goals as well as developmental progressions and learning trajectories derived from empirical research. The GT is designed to inform both the selection of assessment activities for data collection and the interpretation of empirical results. Two primary results of the design process are presented: (a) a goal trajectory for promoting algebraic understanding and (b) the relationships between the trajectory and features of the Common Core State Standards. Implications of the design model for building GTs that can be used to assess student reasoning are discussed. [For the complete proceedings, see ED584829.]