This paper explores the nature of prospective teachers’ noticing of students’ understanding as they analyze and discuss middle school students’ understandings of trapezoids in micro-case videos in the context of geometry. In this exploratory study, the data were obtained from eight prospective middle school mathematics teachers through individual video analysis, reflection papers, and group discussions. The results indicated that the use of purposeful micro-case video designs based on prospective teachers’ background knowledge of quadrilaterals allowed them to be productive in video analyses and discussions. In individual video analyses, prospective teachers attended to various mathematical elements to identify students’ responses but did not always use them to make interpretations of each student’s understanding of trapezoid. In the group discussions of the micro-case videos, in contrast, prospective teachers could provide alternative interpretations of students’ understanding by identifying links between the mathematical elements in students’ responses and the characteristics of students’ understandings. In the group discussions, they provided more detailed and specific instructional actions to support each student’s understanding of trapezoid than their individual video analyses. This study suggests practical implications for teacher education programs on how to use video cases (e.g., firstly, working individually and then having group discussions about the videos) to explore prospective teachers’ professional noticing skills. Considering prospective teachers’ background knowledge of related mathematical contents, this study can also inspire future studies on how to design effective videos about students’ mathematical understanding.

本文探讨了准教师在几何背景下分析和讨论中学生对微型案例视频中梯形的理解时对学生理解的注意的本质。在这项探索性研究中，数据是通过对个人视频分析，反思文件和小组讨论从八名准中学数学老师那里获得的。结果表明，基于准教师对四边形的背景知识，有目的的微案例视频设计的使用使他们能够在视频分析和讨论中发挥作用。在单独的视频分析中，准教师使用各种数学元素来识别学生的反应，但并不总是使用它们来解释每个学生对梯形的理解。相比之下，在微案例视频的小组讨论中，准教师可以通过识别学生回答中的数学元素与学生理解特征之间的联系来提供对学生理解的替代解释。在小组讨论中，与他们各自的视频分析相比，他们提供了更详细，更具体的指导性行动，以支持每个学生对梯形的理解。这项研究提出了关于教师教学计划在如何使用视频案例方面的实际意义（例如，首先，单独工作，然后对视频进行小组讨论），以探索准教师的专业注意技能。考虑到准教师对相关数学内容的背景知识，