In-class debates are frequently used to encourage student engagement. Ideally, after researching both sides of the debate, students will form their own opinions based on what they have learned. However, in a large course of Environmental Science, opinions of students, when surveyed after the debate, were remarkably consistent with the position that they had been assigned. This study aimed to determine whether an assigned debate position influenced student opinion. Prior to being assigned a debate position, 132 students in Environmental Science were polled for their opinions on six controversial issues. Each student was assigned to a position, without regard to their opinion, for a debate on one of the issues. Students researched both positions and constructed arguments and counter arguments for both sides, but only argued one side of the debate in class. One week following the debates, students were again polled for their opinions. Prior to debating, only 41% of students happened to agree with their assigned position, yet following the debates, 77% of students agreed with their assigned positions (p = 0.0000005). This suggests that researching and/or arguing an assigned position in a class debate influences student opinion toward that position. (Contains 1 table and 2 figures.)