This study examined flipped classroom and academic performance among physics students in secondary schools in the Rivers State Metropolis of Port Harcourt. This study was guided by four research questions and four hypotheses. Quasi-experimental pretest-posttest experimental and control group design was used in the study. The study population consists of 17,780 senior secondary school students in 45 public secondary schools in Port Harcourt Metropolis, Rivers State. By simple random sampling, four (4) coeducational schools located strategically in the study area were chosen for the study. A non-randomized sample size of 209 students offering Physics in SS 2 class, comprising 114 male and 95 female students, was selected for the study. An instrument titled Physics Performance Test (PPT) was used by the researcher for data collection, which yielded a reliability coefficient of 0.86 using Spearman-Brown formula. The mean and standard deviation were used to answer the research questions, while the hypotheses were tested at the 0.05 level of significance using analysis of covariance (ANCOVA). The analysis results revealed a significant difference between the mean performance scores of students taught physics using the flipped classroom and those taught using the demonstration method. There was a significant difference between the mean performance scores of male and female students taught physics using the flipped classroom. There was no significant difference between the mean performance scores of male and female students taught physics using the demonstration method. There was a significant interaction effect of instructional methods (flipped classroom and demonstration method) and gender on students’ academic performance in physics. The study concluded that a flipped classroom is effective for improving the academic performance of students in Physics. The combination of instructional methods and gender has a significant impact on the academic performance of students in Physics. In view of the findings, recommendations were made that conferences, seminars, and workshops should be organized by school administrators and other educational stakeholders to prepare teachers on how to include and use flipped classrooms, especially for teaching physics