This theoretical project will examine and describe the close relationship between Piaget'stheory of cognitive development, in particular the formal-operational stage, the topic ofcritical thinking and Anton Lawson's theory of scientific reasoning. Previous researchsuggests that the so-called scientific abilities are crucial for academic success in general andplay a key role in science related careers. The purpose of this study is to create an overview ofthe above described field of study and contribute to the research on to middle- and highschool student's ability to utilize scientific reasoning and how these skills relate to thesyllabus for physics in the Swedish education system at middle- and high school level. Inaddition, I briefly describe a research-based education approach that supports students'development of the ability to think scientifically, the Investigative Science LearningEnvironment (ISLE). Furthermore this project includes an English to Swedish translation ofLawson's Classroom Test Of Scientific Reasoning (CTSR) which is a test developed tomeasure students' ability to apply concrete- and formal-operational reasoning.