Abstract The objective pursued by the present study is to investigate the impact of guided inquiry and traditional methods of teaching on the critical thinking skills among second grade high school students. Given the purpose, a total of 190 second grade high school students were chosen through random, multi-step and cluster sampling methods in the form of 8 classes and placed into 8 experimental and control groups. A pre-test post-test design was administered to the control group. The demographic information was collected by a researcher –made questionnaire and the thinking skills information was determined by Watson - Glaser test. Two- factor covariance method was used for data analysis. Results showed that the guided inquiry method of teaching had significant impact (lower than 0.05) on the critical thinking skills of students in inference and conclusion subscales. The impact of gender factor on the students’ critical thinking was significant, in terms of conclusion and interpretation subscales as well. The impact of interaction between gender and teaching method was also significant in inference and interpretation subscales.
