Although it has been two decades since National Council of Teachers of Mathematics "Standards" were published, research underlines the lack of essential practices for quality reform teaching. The literature also emphasizes the importance of planning in reform teaching although few studies focus directly on the planning of the teacher. This study attempts to shed light on teacher planning through a particularistic case study within a design research experiment which was performed to improve the quality of teaching. In particular, this study aims to extract the planning practices of an expert seventh-grade mathematics teacher before and during instruction on integers. The extracted practices were interpreted through the teaching-in-context theory, which uses beliefs, goals, and knowledge as the backbone of the analysis. The results indicate that five core practices underlay the development of effective planning: preparation, reflection, anticipation, assessment, and revision. Each practice included multiple actions performed in an environment of collaboration. (Contains 1 figure and 1 note.)