On a daily basis, PreK-12 teachers make countless decisions about how to best meet their students' needs through assessment and instruction. However, their ability to justify these decisions is not frequently used as a resource for accountability measures or the evaluation of educational programs. The research presented here, which draws from a sequential explanatory mixed methods study of seven secondary English/language arts teachers' formative assessment practices, delves into how teachers' evaluative thinking occurs in the classroom. Data were collected using the experience sampling method with a series of weekly self-report checklists, as well as semi-structured interviews. Through examining emergent themes from this study and investigating the role of evaluation in education, implications are made for the importance of valuing this process and making this implicit teacher knowledge more explicit.