Considerable evidence has been accumulated in Hong Kong that Learning Study, as a form of action research collaboratively conducted by school teachers and researchers from Higher Educational Institutes, provides a comprehensive platform for school-based teacher professional development. Learning Study is grounded in the Variation Theory developed by Ference Marton. It involves an active collaboration between teachers and academic staff from the Hong Kong Institute of Education. In conducting a Learning Study, teachers, through a rigorous process, first select the topic, then work with the HEI staff to identify the worthwhile object of learning with its critical aspects and collectively design the lesson, which incorporates the application of three forms of variation (V1, V2 and V3). The lesson is taught, video taped and then analysed in a post-lesson conference. A revised plan for teaching the same lesson is then taught by a different member of the research team in his/her class. This process is repeated until all the teachers have taught the lesson to their classes.The Learning Study case will be evaluated and then presented by the teachers to the wider community as part of the dissemination process. This symposium will first provide an overview of Learning Study theory and practice model, then illustrate its actual implementation with several Learning Study cases. The third part discusses how Learning Study builds up an effectively comprehensive platform for classroom teachers to analyze the students' learning achievement, reflect upon their own teaching, develop learning communities and benefit their entire professional development.