The purpose of this action research project was to investigate approaches and techniques that would improve critical thinking skills in history classes at the secondary level. Students demonstrated apathy and boredom in history classes where the emphasis was on rote memorization and the regurgitation of accepted facts and conclusions. The problem was to determine which teaching and learning strategies, techniques, and methods were the most effective in improving critical thinking skills in history. The research methodology consisted in a comparison of the inquiry or interactive method of teaching history with the lecture method. Two groups of high school students were chosen. One group was taught history using the lecture method. The other group was taught using the inquiry method. The criteria were whether students were able to analyze, evaluate, conceptualize, and synthesize information, not just whether they could memorize facts. A comparison of student performances on tests, essays, quizzes, and assignments was used for assessment, evaluation, and comparison. The inquiry strategies included role playing, simulations, re-enactments, examining and analyzing multiple texts, studying oral and visual presentations, analyzing bias by examining different viewpoints and perspectives, and analyzing documents and original and primary sources. The research results demonstrated that when critical thinking skills were emphasized under the inquiry method, students achieved higher scores on tests, quizzes, and assignments and gained a deeper and more meaningful understanding of history. The research results showed that the inquiry method improved critical thinking skills based on the comparison of test and quiz score grades but yielded results when critical thinking skills were integrated with content matter and when students were motivated and engaged and possessed an attitude that placed value on critical and higher order thinking. Finally, the lecture method was more effective in presenting the background and introduction to a topic or issue that the inquiry method was. In conclusion, critical thinking skills were shown to be effective in achieving a more in-depth and meaningful understanding of history by high school students, but relied on the integration of the critical thinking skills with subject content and on student motivation. Educators need to incorporate strategies that emphasize critical thinking skills in order to improve the understanding of history, but the strategies must be integrated with the content matter. Student attitude and motivation must also be stressed. (Contains 2 tables.)