The purpose of this study was to determine the effect of inquiry-based agriscience instruction on student argumentation skills. Argumentation is defined as the student's ability to establish a claim, provide a rationale for steps taken, provide and justify data, recognize alternate conclusions, and provide evidence why the conclusion is correct or the best solution. Developing argumentation skills can aid in developing the next generation of scientists, and help individuals who are not scientists, distinguish evidence from bias. This quasi-experimental study investigated the effect of two teaching methods on student argumentation skills. Inquiry-based instruction was compared to the subject matter approach in 15 agriscience education classes in seven secondary schools across the United States. Univariate analysis of covariance, detected a statistically significant difference between groups on argumentation skills. Those students taught through inquiry-based instruction had higher argumentation skill than students taught through the subject matter approach. (Contains 4 tables and 1 figure.)