This study investigated the effectiveness of integrating the Claim-Evidence-Reasoning (CER) framework with Project-Based Learning (PBL) to enhance the critical thinking skills of agricultural students. In the context of postharvest handling, where decision-making is often compromised by "invisible" biological consequences, this research utilized a quasi-experimental design involving 75 participants divided into an experimental group (n=38) and a control group (n=37). The experimental group was exposed to PBL combined with CER, while the control group utilized standard PBL alone. Both cohorts were evaluated across four domains: analysis, problem-solving, decision-making, and overall critical thinking. Statistical analysis using t-tests revealed that the experimental group achieved highly significant improvements across all variables (p<.05), with the overall critical thinking mean rising from 8.24 to 12.05. In contrast, the control group showed significant growth only in analysis and general critical thinking, failing to reach statistical significance in problem-solving (p=.208) and decision-making (p=.300). A comparison of post-test results confirmed a statistically meaningful performance gap between the two groups (p=.020), leading to the rejection of the null hypothesis for the experimental intervention.

The findings suggest that while traditional PBL fosters foundational knowledge, it is insufficient for developing the high-tier mastery required for complex technical dilemmas. This study underscores the necessity of "engineering" critical thinking into vocational curricula through structured argumentative models to move students from rote procedural application to expert-like professional judgment in agricultural logistics.