The current study aims to investigate whether the instructional approach (flipped or traditional) and gender (male or female) influence students' sense of autonomy, relatedness, and competence, or influence their achievements in high school chemistry. Merrill's First Principles of Instruction theory was used to design the flipped classroom (FC) implemented in this study as recommended by Lo, Lie, and Hew in 2018. The theoretical framework for the study is the self-determination theory (SDT) which posits that satisfaction of individuals' psychological needs for autonomy, competence, and relatedness, enhance their intrinsic motivation and performance (Deci & Ryan, 2002). Ninety participating students who enrolled in two similar high schools located within the same school district in the Northeastern region of the United States were divided equally into flipped and traditional chemistry classrooms. Students were ethnically diverse, spoke English, and identified as either male or female. Both participating teachers (one per each group of students) were Asian-American females, certified to teach chemistry by New York state (NYS), and have at least 20 years of experience in teaching the subject. The current quasi-experimental study employed a series of four two-way ANCOVA tests to analyze the influence of the independent variables (instructional approach and gender), on the dependent variables (academic achievement, and perceived autonomy, competence, and relatedness in chemistry classrooms). Results of the current study indicate that there were no significant differences between students' perception of autonomy, relatedness, or competence based upon the instructional approach or gender, however, there was a significant difference between students' academic achievements based upon the instructional approach. Students in the flipped classroom group scored significantly higher on the post-assessment than students in the traditional classroom group. The current researcher suggests that other variables may have influenced students' achievement in the flipped classroom and further research is necessary. The current researcher recommends that future researchers measure students' situational engagement and motivation in FCs using the experience sampling method and report on qualitative data to provide further insight regarding the efficacy of the FC model. The current study adds to researchers and educators' knowledge new information about the efficacy of the FC model in secondary level, hybrid chemistry classrooms during the COVID-19 global pandemic. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]