The objective of the research is to reveal the effectiveness of using the Roundhouse diagram strategy in teaching Analytic Geometry to develop the reflective thinking skills of secondary language students. To verify the validity of the research hypotheses, the quasi-experimental approach based on the dual- experimental design was adopted. The sample of the research consisted of (60) students of  the first grade secondary from Captain Mohamed Mahmoud Abu Seriaa Official Distinctive language school in Cairo Governorate, and was divided into two groups; (30) students for the experimental group and (30) students for the control group. The Measurement instruments included a pre-post reflective thinking skills test on the chosen units, then the data was processed statistically. The research results had come to the effectiveness of using the Roundhouse Diagram strategy in teaching Analytic Geometry to develop the reflective thinking skills of first grade Language secondary students. There was a statistically significant difference between the average scores of the students of the experimental and the control groups at semantic level (0.01) in the post test of reflective thinking skills in favor of the experimental group.Also, there was a statistically significant difference between the average scores of the students of the experimental and the control groups at semantic level (0.01) in the pre-post applied tests of reflective thinking skills in favor of the post applied test.