Presented are four interpretive reports and a list of current publications of the Mathematics Work Group at the Wisconsin R&D Center. The first interpretive report gives a brief overview of their work. Reports two through four are concerned with individual interviews, carried out during a longitudinal study, in which primary children are asked to solve a variety of verbal addition and subtraction problems. Report two considers correctness of answers along with some interpretations and implications of data collected thus far. Reports three and four consider addition and subtraction, respectively. The strategies and processes used to solve the problems are discussed and the findings to date are listed. (MK)