Summary: Middle school mathematics classrooms are changing. The curriculum has changed as well. Instead of an annual return to previously encountered topics, many middle school students encounter mathematics of a varying nature, characterized in "Principles and Standards for School Mathematics" (NCTM 2000) as the five Content Standards of Number and Operations, Algebra, Geometry, Measurement, and Data Analysis and Probability. As students explore these multiple areas of mathematics, activities in some texts encourage the use of various technologies such as graphing calculators, spreadsheets, or dynamic geometry systems to help enhance and extend studentsâ€™ learning experiences. Of these many important advances, graphing calculators are particularly notable for their portability, ease of use, relatively low cost, and extreme functionality. In this article, the authors highlight several graphing calculator activities and focus on four powerful ways to use this technology as a tool to explore mathematical ideas: (1) collecting or generating raw data; (2) examining multiple cases; (3) providing immediate feedback; and (4) showing graphical and numerical displays. The many uses of handheld technology for learning math involve specialized knowledge that is framed as TPACK: technology, pedagogy, and content knowledge. TPACK goes beyond the teacher having personal knowledge of how to use technology or being proficient with it. The authors describe how to apply TPACK to a lesson on the meaning of angles. (Contains 4 figures.) (ERIC)