Through a series of in vivo experiments, I tested the effects of using prompted self-explanation to help adult English language learners acquire the English article system (e.g., teaching students the difference between "I saw a dog" versus "I was the dog"). In the pilot study, I explored different modalities of self-explanation (free-form versus menu-based), and in Study 1, 1 looked at transfer effects between practice and self-explanation. In the studies that followed, I added an additional deep processing manipulation (Study 2: analogical comparisons) and a strategy designed to increase the rate of practice and information processing (Study 3: worked example study). Finally, in Study 4, I built and evaluated an adaptive self-explanation tutor that prompted students to self-explain only when estimates of prior knowledge were low. Across all studies, results show that self-explanation is an effective instructional strategy in that it leads to significant pre to posttest learning gains, but it is inefficient compared to tutored practice. In addition to learning gains, I compared learning process data and found that both self-explanation and practice lead to similar patterns of learning and there was no evidence in support of individual differences. 
