This article describes an effort to explore and enhance argumentation skills of Taiwanese grade 6 students through instruction in socioscientific issues. An experienced elementary school teacher was given 8 months of personalized instruction on argumentation skills and socioscientific issues, then subsequently implemented a 17-h classroom unit on the establishment of Ma-Guo National Park. His students learned to establish claims and warrants, construct counterarguments, offer supportive arguments, and provide evidence for each one. Data consisted of student responses to questionnaires and individual follow-up interviews. A multiple regression analysis revealed that success in learning argumentation skills was not substantially related to pre-instruction argumentation skills, but significantly related to the student ability levels. High-ability students were significantly better than low-ability students at generating complete arguments. Most students elaborated their arguments, and more high-ability students offered rebuttals after instruction. However, even these high achievers did not completely understand the meaning of evidence and often misused supplementary warrants as evidence.