This paper describes a development and evaluation process used to create teacher education materials that help prepare middle and secondary mathematics teachers to teach data analysis and probability concepts with technology tools. One aspect of statistical reasoning needed for teaching is the ability to coordinate understandings of center and spread. The materials attempt to foster such coordination by emphasizing reasoning about intervals of data rather than a single focus on a point estimate (e.g., measure of center). We take a close look at several different data sources across multiple implementation semesters to examine prospective mathematics teachers’ ability to reason with center and spread in a coordinated way. We also look at the prospective teachers’ ability to apply their understandings in pedagogical tasks. Our analysis illustrates the difficulty in both achieving this understanding and transferring it to teaching practices. We provide examples of how results were used to revise the materials and address issues of implementation by mathematics teacher educators.