This experimental study examined the effects of pre-tests and feedback on learning outcomes in a five-week massive open online course (MOOC). The participants (N = 399) were adults from around the world who self-enrolled in the American Museum of Natural History's (AMNH) climate change MOOC (called "Our Earth's Future") offered on the Coursera platform. Participants were randomly assigned to one of four conditions. Learners in the first treatment group took pre-tests without receiving feedback. Learners in the second treatment group took pre-tests and received basic (correct/incorrect) feedback. Learners in the third treatment group took pre-tests and received elaborate feedback. The fourth group was the control. Post-tests were administered to measure learning outcomes. Additionally, we examined links among self-efficacy, persistence, and outcome measures. Of the 606 participants assigned to the four conditions, 399 met the criteria for inclusion in the final analysis. Results of this study indicate that: (1) among all users in a MOOC, pre-tests and feedback do not affect learning outcomes; (2) the presence of pre-tests significantly and negatively affects persistence and completion, deterring some participants from progressing through the course; (3) among those who do persist and complete the course, those who take pre-tests achieve higher learning outcomes than those who do not; and (4) among those who take pre-tests, there is a positive, cumulative effect of persistence (module completion) on learning outcomes. These findings represent a new contribution to the literature on assessment and feedback, expanding the field to include adult participants from around the world who enrolled in a self-paced, not-for-credit online science course. The results pave the way for future research in this area with this population and have a direct practical application for online course developers, offering them information to help improve student learning outcomes and engagement. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]