This study investigated the modalities of science teaching practice and students' pedagogic subject positioning through the linguistic features of science classroom discourse and the discursive interaction. For this purpose, this study sought to develop a methodology for classroom discourse analysis, the TMARC (Triangular Model of Analyzing discourse Register and language Code). Applied to a middle school science classroom, the TMARC revealed that there were six types of teaching modalities during the classroom practices in spite of the teacher's predominant didactic teaching and that there existed the diverse variation types of the teaching modalities according to a temporal order. In addition, we found four types of pedagogic subject positioning through the application of TMARC. We also argued that the pedagogic subject positioning of a successful science learner was implemented in the discourse language codes of personal collaborative open discourse, positional collaborated open discourse, and personal collaborative controlled discourse. Each of these related to the science teaching modality in which student centeredness was emphasized. Thus, this study suggests that a science teacher's competency related to managing classroom discourse can control students' pedagogic subject position and, by extension, contribute to students' science learning. (Contains 2 tables and 7 figures.)