This paper describes how a team of teachers and researchers in Hong Kong worked together to develop a research lesson on electro-chemical series in a Learning Study at Secondary 4 level in the subject of Chemistry. Learning study is premised on a conceptual framework that builds on three types of variation: variation in students' understanding of a specific object of learning (V1); variation in teachers' understanding and ways of handling the object (V2); and the use of patterns of variation based on the Theory of Variation (V3). The study reported in this paper illustrates how the conceptual framework, in particular, the use of patterns of variation, helps to enhance student learning. In this study, the same teacher taught the research lesson in two cycles to two Secondary 4 Chemistry classes in the same school. The two cycles of research lesson were videotaped, analyzed and triangulated with the student learning outcomes in a diagnostic test administered before and after the lesson, and a post-lesson group interview with a sample of students. Whereas the theoretical framework of variation was employed to analyze what patterns of variation were created and hence what was made possible to learn in the lessons, the results of the pre- and post- test were compared to trace the students' progress in categories of questions that measured for their understanding. In the research lesson, patterns of variation which served the functions of ìseparation and ìgeneralization were used to help the students to understand how the electro-chemical series is derived, and to discern that the order of the metals in the series and the potential difference between any two given metals are constant and independent of the reference metal used. The student learning outcomes showed that there was substantial growth in the students' understanding of these concepts.