The LPPSync project (Learning Progress Profiles Synchronized for Networked Wireless Devices) at North Carolina State University is developing an Interactive Diagnostic Assessment System for K–8 mathematics. LPPSync integrates empirically validated mathematics learning trajectories with corresponding diagnostic assessments that focus on critical topics of rational number reasoning—the foundation of algebraic preparation. The environment is delivered through Web-browsers on mobile devices (tablets and laptop computers) via a centrally-hosted dynamic database on the North Carolina Education Cloud server system. Assessment results are instantaneously processed and scored, with feedback rapidly provided to teachers and students. LPPSync provides mathematics diagnostic tools for formative use, and provides explicit guidance to support instruction. The system includes a diagnostic, a practice, and a targeted intervention mode. In two modes, students can collaborate through chat and work-sharing tools. This exhibit will highlight the design, components, and research methodology and use model of the LPPSync system, and will include live access to the system’s diagnostic and practice features.