In this article, two problems associated with the expectation that teachers use contemporary assessment techniques are examined. The first problem relates to teachers' sense-making of assessment data. Illustrative cases revealed that teachers' processes of interpretation of students' understanding, knowledge and learning of mathematics draws on a rich knowledge base of understandings, beliefs, and attitudes. Consequently, the process of sense-making of students' mathematical understandings involves ambiguity and difficulty. The second problem relates to ways of helping teachers adopt contemporary assessment approaches. A professional development activity served as the example examined. Three aspects of what the course instructor promoted with respect to contemporary assessment were analysed: (1) the assessment methods and tools advocated in the course, (2) the degree to which the integration of assessment with instruction was promoted, and (3) the purposes for assessment highlighted in the course. It appeared that attention was paid to the use of contemporary assessment tools, but this was associated with traditional assessment purposes. Learning to use the new assessment tool did, however, influence instruction and fostered greater integration of assessment and instruction than before--a characteristic of contemporary assessment. The article concludes with a discussion of the current expectation that teachers use assessment data to improve instruction. (Contains 1 footnote.)