This study examined what happened when 65 undergraduate prospective secondary level teachers across content areas evaluated the reliability of four online sources about climate change: an oil company webpage, a news report, and two climate change organizations with competing views on climate change. The students evaluated the sources at three time intervals based on 1. a screenshot of each source; 2. full web access to each source and prompted with critical questions to answer; and 3. after a whole class discussion about each source. Having the opportunity to evaluate the sources three times led students to modify their reliability ratings. Findings also reveal challenges some participants had differentiating between facts and opinions as well as distinctions in what they determined to be evidence in a source.