Memory retrieval is well known to modify retention of not only retrieved material, but also related, non-retrieved material. This dissertation consists of two manuscripts that investigated retrieval phenomena in the learning of foreign language vocabulary and science education material. The testing effect--the retention benefit of practicing retrieval compared to studying-- and the pretesting effect--incorrectly guessing a target before learning compared to studying-- demonstrate the advantages of retrieval-based learning, but no extant theories have accounted for both of these effects. In Chapter 1, we investigated an error-driven learning account whereby retrieval-based learning serves to "stress test" the memory system, allowing it to learn to better predict a target from a cue, whereas in studying, there is no opportunity for the system to form a prediction. We predicted that inserting a small temporal "gap" between a foreign language word and its English translation should enhance retention when compared to simultaneous, "no gap," presentation. In four experiments (N = 287) we consistently observed that "gap" conditions benefitted retention compared to "no gap" conditions, which supports the error-driven learning account. We observed that a gap as short as 600 ms benefitted retention one day later, one minute later, and in a pure list design. In Chapter 2, we investigated the sequalae of retrieval practice for non-practiced educational science text material. Some evidence suggests that retrieval practice of main ideas would lead to greater retention of non-practiced information, whereas other evidence suggests that retrieval practice of peripheral information would lead to impaired retention of non-practiced information, when compared to a control group that did not practice retrieval. In two experiments (N = 360) we observed robust testing effects, but we did not observe robust differences in non-practiced material, suggesting that the kind of focal retrieval practice used here has focal effects on science material retention. [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.]