There is evidence that school leaders are using test score data for decisions about everything from the curriculum to what is served for lunch. Research suggests that staffing too is data-driven, with principals using test score data to hire, assign, and develop their teachers. Semi-structured interviews with principals and other school actors in 10 case study elementary schools show that while principals report using test score data as they assign students to classes, they are not using the assignment process as a strategy for overall school improvement, but instead to ensure within-class heterogeneity and a sense of "fairness" among teachers.