Calls for change in mathematics instruction and continuing professional development to foster such change is not new. Yet there have been recent calls for professional development for the topic of probability, and particularly for research to monitor and probe professional development programs (Watson, 1992). Several reports at the 1995 PME outlined the specific nature that professional development can take. For example, comparison of four teachers in the ARTISM program showed that, although the external input was the same, their individual change depended on varying local factors such as collegial support (Peter, 1995). Research was undertaken to compare two Victorian teacher professional development programs: Learning in Primary Science (LIPS) and Mathematics in Schools (MIS). As well as different discipline content, MIS and LIPS differed in their implementation. Analysis of questionnaire data showed that the needs of teachers differed for mathematics and for science, and thus the resulting professional development content reflected this difference. However, further analysis found that some mathematics topics such as Chance and Data attracted similar responses to those of science. Professional development in these schools was similar to that of science, where teachers responded favourably to specific curriculum content knowledge and activities for the classroom. This contrasts with a process approach that appeared to meet the needs of teachers involved in topics such as number and measurement. Early NUD.IST coding of interviews of teachers involved in MIS Chance projects supports this result and gives some suggestions why this might have occurred. Firstly, the topic of probability is new to most primary teachers, and secondly, probability invites a range of concepts from naive to sophisticated.