Understanding when it is appropriate to make causal inferences from a statistical result is a fundamental skill for science literacy. Prior research has concentrated on erroneous causal judgments about observational studies, but there is little research on whether people understand that experiments provide stronger justification for causal claims. Our study tested the efficacy of an intervention at improving students' ability to discriminate between correlation and causation. Students were taught how to use causal diagrams to illustrate possible explanations for a statistical relation in an experiment versus an observational study. To evaluate the intervention's efficacy, intro psych (Experiments 1-3) and research methods (Experiment 1) students decided whether to make causal inferences about hypothetical observational studies and experiments. In Experiment 1, we tested multiple methods of instruction to see which worked best. Intro psych students learned more when they completed practice problems that involved generating self-explanations, whereas research methods students learned more from making analogical comparisons or reading worked examples. Critically, we found that students struggled with identifying the study design, which is the first step in correlation-causation discrimination. In Experiment 2, we added instructions to the Self Explanation intervention about how to identify observational studies versus experiments. Our modifications did not improve this skill nor students' ability to discriminate between correlation and causation. The most successful intervention was in Experiment 3, which explicitly pointed out that people often make errors when evaluating evidence from observational studies and repeated the importance of considering study design when making causal judgments. A second goal of Experiment 3 was to test the influence of students' expectations about the direction of the statistical relationship on their evaluation of the evidence. Students made more causal inferences about study outcomes that were in the same direction as their prior beliefs than outcomes they thought were implausible. After the intervention, students still used their prior beliefs to decide whether to make a causal judgment, but they also more strongly considered the study design in their evaluation of evidence. In general, our intervention improved students' understanding of causality, but its efficacy may also depend on their prior knowledge. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]