This article describes a lesson study on the area of a parallelogram for year 7 students. In Singapore, students in secondary schools are streamed into ability bands. Normal (Academic) is the label for the middle band. The teachers were convinced that Lesson Study provided a valuable platform for professional development. The authors followed the key steps of the Lesson Study process as delineated by a number of writers. These steps include: (1) identifying the problem and setting goals; (2) designing the lesson of focus; (3) teaching, observing, and refining; and (4) sharing of results. As a Lesson Study team, the authors focused on the topic of Mensuration and subsequently zoomed-in further to the lesson on "area of parallelogram" as the Lesson of focus. They discuss their experiences in teaching the topic "Area of Parallelogram", especially the difficulties they faced in helping their students understand how to derive the formula "base x height". In the Singapore context, "height" is taken to mean "perpendicular height". The aim of this paper is to share the learning experiences of the team as they underwent the Lesson Study process. (Contains 6 figures.)