In this paper, the development of sixth grade students' critical thinking skills in science courses is discussed relatively to the contribution of the integration of aspects of History of Science into instruction. Towards this direction a project on electromagnetism was designed and implemented aiming to engage primary school students in a critical examination of knowledge (importance, complexity and human implications) by generating argumentation and discussion in their classrooms. The "Test of Everyday Reasoning (TER)", which targets the core critical thinking skills identified in "The Delphi Report" consensus, was translated and standardized for the Greek population in order to be used for the project's assessment. A pre-post analysis was conducted for the experimental group and the control group. The encouraging results regarding critical thinking skills development are supportive to the integration of aspects of History of Science in science courses.