This paper aims to compare the various definitions of disciplinary skills and to see if their differences have an influence on the creation and the choice of items in two international investigations: the Trends in International Mathematics and Science Study (TIMSS) and Program for International Student Assessment (PISA). Thus, our interest focuses on the perspective and the philosophical orientation that guide the construction of these evaluations and which results from a consensus among the participating countries. We will introduce the aims of the TIMSS and PISA before summarizing their respective structure and presenting in more details their respective definitions of disciplinary skills as well as their item development and choices.