This study designed and examined the effects of Metacognitive and Argument-Driven Learning Environment (MADLE) in cultivating students' reflective thinking skills. The study involved a group of third-year Biological Science Education students (n=23) in a state university in the Philippines. The study employed a mixed-method approach, where both quantitative and qualitative data were collected and analyzed to answer the research question. Specifically, one-group pretest-posttest design was used under the paradigm of pedagogical action research. The quantitative data were obtained from a 16- item pre- and post-Reflective Thinking Questionnaire while qualitative data were culled from classroom observations and focus group discussions. The Wilcoxon Signed Ranks Test was utilized to determine significant changes in students' reflective thinking skills. Findings showed an insignificant difference in students' reflective thinking skills prior to and after their fourweek exposure to MADLE. However, the multiple sources of data yielded from students' higher posttest mean scores in each level of reflective thinking skills, classroom observations, and responses in the focus group discussion imply the efficacy of MADLE in stimulating and supporting students' reflective thinking skills. Hence, it is recommended to integrate MADLE in improving instructional practices that will engage students in reflective thinking practices.