Most educational studies highlight the gender gap in Science, Technology, Engineering, and Mathematics (STEM). Female students' interest and success in STEM are behind their male peers, especially in chemistry and physics classes. Females are less likely to pursue a STEM field in college. In addition, few women want to be scientists and engineers. The gender gap in STEM may be a result of traditional science teaching methods. Female students' expectations are not met, and as a result, their science interest decreases in these classrooms, as well as not pursuing STEM careers in specific chemistry, engineering, and physics. There is an increase in research and curriculum reform movements containing socioscientific issues (SSI) extending worldwide. SSI provides an opportunity to engage students in critical thinking. SSI-based science classrooms are based on real-world problems like climate change, genetic modification, and vaccination. Integrating SSI into science classrooms as a revolutionary method might renew the practices of our traditional science classrooms. However, few SSI-based educational research studies have focused on the gender gap issue. This dissertation investigated 216 middle and high school students' experiences in SSI-based classrooms with a mixed-methods approach. I investigated Model-Evidence Link diagram's effectiveness on the shiftiest in students' plausibility toward scientific model and scientific knowledge gaining in the quantitative part. I examined their experiences in SSI-based classrooms with the open-ended question survey in the qualitative part. SSI-based science activities provided gender equity conditions in science classrooms. Both genders evaluated the scientific model as more plausible by eliminating the alternative model as less plausible, and they gained scientific knowledge about Climate Change and Wetlands. The MEL diagram seemed more effective for the students' positive plausibility shifts toward the scientifically accepted model. Also, both genders had positive experiences in SSI-based classrooms in general. However, female students did not want to continue a STEM career except biomedical sciences. MEL design can be renewed by adding some initial and interval short activities and using some SSI topic-related posters and objects to prepare students for critical thinking and keep them more engaged during the activities. Also, adding student interviews and live recording the student discussions might give an understanding of the collaboration and student experiences in the SSI-based classrooms. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]