Although positive effects of lesson study on teachers learning are reported, only some studies have investigated teacher noticing as an analytical tool for supporting teachers with an explicit focus, as in LS, and more empirical evidence is needed. This qualitative interpretive case study design aims to investigate the noticing processes of a group of mathematics teachers conducting a lesson study cycle focused on teaching algebraic expressions using manipulatives in middle school. Data is collected through the audio recordings of the participants' lesson study meetings. Participants were six elementary mathematics teachers who attended a graduate course selected based on voluntariness. This study aims to incorporate Lee and Choy's (2019) teacher noticing framework with Sfard's (2008) commognitive theory, which views learning "as changes in discourse" and noticing as a "discourse structure" covering observation, interpretation, and reasoning processes (van Es, 2011). Results showed that teachers focused more on aspects of students' learning than issues of their instructional practice. However, their noticing was mostly related to future decisions and actions regarding issues of teaching methods and sequencing of the lesson, whereas teachers' dominant noticing form related to students learning was interpretive. Results illustrate the applicability of these noticing frameworks as an analytic tool where noticing is conceptualized as a pedagogical discourse for the analysis of a lesson study review discussion by a group of mathematics teachers who focus on teaching algebraic expressions.