Mathematics education needs measures that can be used to research and/or evaluate the impact of professional development for constructs that are broadly relevant to the field. To address this need we developed the Priorities for Mathematics Instruction (PMI) survey consisting of two scales focused on the constructs of Explicit Attention to Concepts (EAC) and Student Opportunities to Struggle (SOS) -- which have been linked to increased student understanding and achievement. We identified the most critical assumptions that underlie the proposed interpretation and use of the scale scores and then examined the related validity evidence. We found the evidence for each assumption supports the proposed interpretation and use of the scale scores. [For the complete proceedings, see ED630060.]