Since 2016, Park School in Denmark has consistently used Japanese lesson study as an approach to the professional development of its mathematics teachers. The school has moved beyond the initial adaptation of lesson study, and no longer includes external support. In this article, I investigate how three groups of teachers participated in the maturing lesson-study phases, especially the reflection phase. I apply social practice theory, particularly the concepts of figured worlds and improvisation, to examine the groups’ improvisation of artefacts and actions during lesson study, and the mature, valued outcomes. This study explains how and why the mature lesson-study efforts at Park School offer predominantly superficial learning opportunities to students and teachers alike. It concludes that in countries unaccustomed to lesson study, external support (or other external knowledge sources) is also important at the mature stages of its adaptation. This study proposes three activities that offer such support.

自 2016 年以来，丹麦帕克学校一直将日语课程学习作为其数学教师专业发展的一种方法。学校已经超越了课程学习的最初适应，不再包括外部支持。在本文中，我研究了三组教师如何参与成熟的课业阶段，尤其是反思阶段。我运用社会实践理论，特别是想象世界和即兴创作的概念，来检查小组在课程学习期间对人工制品和行动的即兴创作，以及成熟、有价值的成果。这项研究解释了帕克学校成熟的课程学习努力如何以及为什么为学生和教师提供了主要是肤浅的学习机会。它的结论是，在不习惯课程学习的国家，外部支持（或其他外部知识来源）在其适应的成熟阶段也很重要。本研究提出了三项提供此类支持的活动。