<![CDATA[Science instruction in Indonesian secondary classrooms often positions students as passive recipients, limiting opportunities for evidence-based reasoning. This gap is particularly acute for critical thinking development, which is central to biology and science education yet underexplored in the context of air-pollution-based inquiry in Indonesia. This study examined the effect of an inquiry learning model based on real-life problem solving (IL-RLPS) focused on air pollution on the critical thinking skills of 31 Grade VIII students at a public junior high school in Bandung, Indonesia. The study used a one-group pretest–posttest design conducted over two class meetings through six learning phases: stimulation, problem formulation, data collection, application, communication, and reflection, culminating in the design of an air filter prototype. Student’s critical thinking skills were measured using a 10-item test, validated by two science education experts (content validity ratio = 0.89), supported by an implementation observation sheet and a seven-criterion project rubric (α = 0.83). The Wilcoxon signed-rank test showed a statistically significant improvement (Z = −6.853; p < .001) with a large effect size (r = 0.87). The overall N-gain was 0.16 (low), largely attributable to a ceiling effect among seven high-scoring students; excluding these students raised the N-gain to 0.21, with 17 students recording a mean gain of 0.57 (moderate). Interpretation and knowledge-transfer indicators showed the strongest gains, whereas solution evaluation and investigation design-higher-order metacognitive demands-remained comparatively underdeveloped. These findings suggest that IL-RLPS is a promising, low-cost strategy for cultivating critical thinking in biology classrooms, particularly for students with initially low-to-moderate ability, provided that future implementations extend beyond two sessions and incorporate explicit scaffolding of evaluative reasoning]]>
