This article examines how SEAs in three states designed, installed, and operated statewide, longitudinal student information systems (SLSIS). SLSIS track individual students' progress in K-12 schools, college, and beyond and link it to individual schools and teachers. They are key components of the information infrastructure of test-based accountability. Drawing on science and technology studies, this study documents the strategies SEAs use to assemble and coordinate the vast amounts of technology and people across and beyond the educational system needed to collect, process, and disseminate test-based accountability data through SLSIS. We find that while SLSIS expand state power through what we refer to as informatic power, SEA control over these systems and the data they produce depends on whether SEA staff can manage the competing interests of federal, state, district, and external actors. SLSIS are thus sites of the ongoing contestation of state power within and beyond the educational system. (Contains 1 table.)