The purpose of this study was to investigate the effects of learning activities based on argumentation about "Force and Motion" unit on conceptual understanding and views about establishing thinking friendly classroom environment of 7th graders. The study was conducted with total 39 students (20 students in experimental group and 19 students in control group) in a secondary school. The experimental group received learning activities based on argumentation while the control group received regular science learning depending on the current science curriculum for over five week period. Both groups were given Force and Motion Concept Test and Thinking Friendly Classroom Scale before and after the instruction. Besides, six students from the experimental group were interviewed after the instruction about conceptual understanding and thinking friendly classroom features by a form developed by the researchers. The results showed that there isn't a significant difference between conceptual understandings of experimental and control group students. Besides, it was found that there is a significant difference between thinking friendly classroom scale of experimental and control group students in favor of experimental group. Moreover, the results of the interviews conducted with six of experimental group indicated that they feel themselves in thinking friendly classrooms and with a fine conceptual understandings are fine although they have some misconceptions.