A cognitive process approach is applied to this discussion of the nature and relationship of skills, thinking, and social studies knowledge. To make understanding explicit, the paper addresses: (1) the meaning of cognitive skills and their role in thinking; (2) generic versus specific skills; and (3) implications for the National Assessment of Educational Progress (NAEP). Critical thinking is a skill frequently associated with social studies learning. However, attempts to detail a task analysis of critical thinking skill have met with problems: It is difficult to define a constant concept of thinking; thinking is rarely a process of linear steps; thinking about one question tends to raise others; and thinking cannot be divided into pieces and reconstructed. Skills and thinking are not synonymous and should not be treated as such for assessment. Despite the assumption that thinking skills are generic and transferable from one subject to another, there is evidence that the development of thinking skills is highly knowledge dependent; the separation of subject matter content and thinking process is arbitrary and misleading. Social studies test items should assess either the application of a skill, or the selection and application of the appropriate skill. To assess critical thinking, assessment of thinking and not assessment of separate skills is needed. Test items should include social studies subject matter, and former NAEP items should be retained for comparative analysis. (GDC)