In this study, educational dialogue is explored through informal formative assessment and dialogicity. We enhance the understanding of informal formative assessment and dialogicity by considering their relationship. Even though the interconnection of informal formative assessment and dialogicity is acknowledged, it has not been explicitly examined in research on educational dialogue. The data consists of video-stimulated joint reflections between mathematics student teachers and a teacher educator. The reflections were part of a teacher education program integrated in a mathematics pedagogic course. Conversational analysis was conducted to detect interactional patterns and indicators that emerged from the data. The findings show how the presence and absence of single informal formative assessment moves, such as recognizing and using learners’ ideas, contribute differently to dialogicity and educational dialogue.