The purpose of this study was to investigate the relationships between students conceptions of the nature of science and their reactions to evidence that challenged their beliefs about socioscientific issues. This study involved 41 pairs of students representing ldquo critical cases rdquo of contrasting ethical viewpoints. These 82 students were identified from a larger sample of 248 students from 9th and 10th grade general science classes 11th and 12th grade honors biology honors science and physics classes and upper-level college preservice science education classes.