CCT collaborated with Dr. Herb Ginsburg, a leading interpreter of children's understandings of mathematics, and Wireless Generation, a developer of educational applications for handheld computers, to develop handheld diagnostic applications for mathematics learning that address basic arithmetic skills using multiplication as a model. As part of the project, the team created associated professional development materials that support teacher use of the applications. The team also conducted several small studies to determine the tools' reliability and the impact on teachers' thinking about mathematics and instruction.