Online communities of practice (online CoP) have emerged as a viable method for teacher professional development regarding the emphasis on teacher networks for effective professional development and the elimination of some restrictions with online learning. Moreover, most technology integration studies examine teacher-centered technology integration which is the practice of learning-from-medium. On the other hand, there are limited research studies that investigate teachers' professional development process on student-centered technology integration through CoP, and the role of student-centered technology integration in the classroom from the perspectives of teachers. Therefore, this exploratory single case study aimed to investigate the effects of online CoP for teacher professional development program about integrating technology as cognitive tools on elementary mathematics teachers' student-centered technology integration mathematics teaching, and opinions of the teachers' about CoP program. In this study, 24 math teachers took part. The qualitative data sources of the study, online discussion logs, lesson plans, and interviews, were analyzed through the Interaction Analysis Model, a Constructivist Learning Environments Checklist developed by authors, and thematic analysis, respectively. The results showed the indicators of the constructivist learning environments in the lesson plans the teachers prepared and knowledge construction throughout the online interactions. The findings also highlighted the teachers' experiences in an online CoP as they learned how to implement cognitive tools in their practices. Based on the findings several recommendations were provided for designing teacher professional development programs and creating and implementing lesson plans that incorporate cognitive tools.