We investigated the social validity of the NECC Core Skills Assessment (NECC-CSA) with parents and professionals as participants. The NECC-CSA is a measurement tool consisting of direct and indirect measures of skills important to all individuals with autism, across the lifespan. Participants (N = 245) were provided with a list of 66 skills, 47 of which were Core Skills from the NECC-CSA, and were asked to indicate which items they considered to be foundational. Participants endorsed items from the NECC-CSA as foundational skills, more than they endorsed the other items. Differences between parents and professionals are described and detailed with respect to individual assessment items. The NECC-CSA consists of socially validated skills that can be taken as a starting point for programs of instruction for individuals with ASDs.