The article presents the results of two cross-sectional studies that investigate teachers' skills in using various techniques of assessment in mathematics by taking into account the four phases of assessment. The five dimensions of the dynamic model are also taken into account in proposing a framework for measuring teacher skills in assessment. These two studies were conducted in different countries, Cyprus and Greece, and data were collected through a self-report questionnaire. Semi-structured interviews were also conducted and the internal validity of the study was supported. Using the Rasch and the Saltus models, it was found that assessment skills can be grouped into four types of assessment behavior which are discerned in a distinctive way and move gradually from skills associated with everyday assessment routines to more advanced skills concerned with differentiation in assessment. Comparing the findings of the two studies, it is shown that the same stages were identified through both studies. Implications of these findings for further research are drawn.