This exploratory multi-case study investigates the types of teacher performance data principals consider and collect when evaluating teachers. Data come from public school principals (N = 10) in the U.S. state of Michigan and includes: interviews (n = 30), observations (n = 20), and artifacts collected in 2016 and 2017. Additionally, specific teacher evaluation district documents inform this study. Findings show principals collect ongoing observational data of teacher instruction and consider all teacher observations when evaluating teacher performance. Additionally, principals consider teachers' efforts at improving their practice when evaluating teacher performance. Implications for policy and practice are discussed.