This study investigates the effects of argument stance on knowledge inquiry skills. Sixty-two participants were assigned to three argument stance conditions (proponent, opponent, or control) to receive scaffolded argumentation practice on two science issues in random order. After the argumentation treatment, participants were asked to write down their own opinions regarding the claim. Their responses were analysed according to argument structure, argument content, methods of refutation, and number of new propositions. Results revealed that taking a proponent's stance increased the use of evidence in argumentation, while taking an opponent's stance enhanced both the use of evidence and alternative-based refutations to the claim, number of falsifications, and number of new propositions. This implies that arguing from an opponent's stance may increase the search for multiple causes behind observed phenomena and the need for evidence, thereby alleviating the confirmation bias in thinking.