In this study, the authors examined their efforts to teach beginning teachers’ formative assessment practices, specifically to elicit and interpret students’ mathematical thinking. This study surfaced a number of important ideas about scaffolding students’ learning of practice in the context of a commonly used teacher education assignment. The findings reveal that each scaffold examined in this paper appeared to support and shape student performance. Furthermore, fixed scaffolds designed in advance and scaffolds crafted in the moment based on the unfolding circumstances were both useful in supporting and shaping student practice.