Teachers are key users of classroom assessment data; however, their needs and preferences are often overlooked in the design and development of the assessments themselves. We used principles of Human-Centered Design (HCD) to systematically solicit, study, and integrate teachers' needs in the design and development of a classroom-based early mathematics assessment. We recruited 18 teachers to participate in a series of research activities that align with HCD methodology. Data informed the articulation of the use case and test specifications, thereby elevating teachers' voices to improve test-development decisions that consider the end users from the start.