This paper describes how one group of students came to reason about data while developing statistical understandings related to exploratory data analysis. Episodes taken from a 7th grade classroom in which a 12-week teaching experiment was conducted are presented. One of the goals of the teaching experiment was to investigate ways to support middle school students' development of statistical reasoning proactively. The use of computer tools was viewed as an integral aspect of statistical reasoning rather than an add-on. Two computer tools were designed with the intention of supporting students' emerging mathematical notions while simultaneously providing them with tools for data analysis. The intent of the instructional sequences developed in the course of the teaching experiment is outlined first. The rest of the paper consists of descriptions of episodes from the classroom that highlight students' development of sophisticated ways to reason about data.