Our main purpose was to see if people’s beliefs predicted their effectiveness at evaluating an argument. Can students evaluate particular arguments that they either agree or disagree with, and do their beliefs bias this ability? We also sought to see if logical reasoning skills mediated the relationship between beliefs and argument evaluation. Students were prescreened for their beliefs about spanking and television violence effects. Only those with strong beliefs were tested. Students completed multiple choice pre-knowledge tests. Next, students read sentences with an argument claim and a reason, and had to judge whether the reason supported the claim. The questions of the reasoning test were taken from old LSAT exams. The results showed that belief in an argument did not affect how well a person could evaluate the validity of a given argument. However, belief in the argument biased people into accepting it as valid even if it wasn’t, and disbelief biased them into discrediting the argument as false even if it wasn’t. With reasoning ability, good reasoners were better able to judge the validity of the arguments, but were no more or less biased in responding.