Using a framework of assessment literacy that included teachers' view of learning, knowledge of assessment tools, and knowledge of assessment interpretation and action taking, this study explored the assessment literacy of five experienced middle school teachers. Multiple sources of data were: teachers' predictions about students' ideas, students' written and verbal responses to assessment tasks, teacher background questionnaire, and a videotaped teacher focus group. We investigated middle school teachers' predictions, interpretations, and recommended actions for formative assessment in genetics. Results documented a variety of ways that teachers would elicit students' ideas in genetics, focusing on discussion strategies. Findings showed how well teachers predicted student conceptions compared to actual student conceptions. We also found that teachers mostly described general topics they would use to address students' alternative conceptions. Less often, they explained specific content they would use to challenge ideas or pedagogical strategies for conceptual change. Teachers also discussed barriers to addressing ideas. Teacher professional development should provide more support in helping teachers close the formative assessment cycle by addressing conceptions that are elicited with assessments.