"Notes & Reflections" offers practical information--ideas, strategies, tools, and resources--about topics of special interest to professional developers who are working to improve school performance. Today, professional development services to schools are provided by variety of people: teacher leaders; principals; and district, regional, and state education staff--to name just a few. If you are one of these providers, "Notes & Reflections" will help you build our capacity to plan and implement powerful professional development. This issue of "Notes & Reflections" provides a recipe for school improvement based on data exploration. The main ingredients are the data themselves: useful information about schools and students. The recipe has four steps: (1) Prepare for data exploration: The process begins with promoting a data culture and forming a team that will examine the data; (2) Collect and organize the data: The team identifies the relevant data, gathers it together, and organizes it for analysis; (3) Analyze the data: The team reviews the data and looks for important patterns--It identifies specific programs or student groups most in need of improvement; and (4) Explain the results: The team uses data to generate hypotheses and explain the underlying causes of the areas needing improvement. Suggestions for additional reading and tools and resources are also provided. (Contains 7 tables and 3 figures.) [Jonathan Margolin was a contributing author for this issue.]