To maximize the effectiveness of instructional explanations, they should be tailored to an individual learner. However, instructors are often not able to collect diagnostically relevant information about a learner to individualize their explanations. This is particularly true in computer-mediated settings where it is more difficult to thoroughly assess a learner's understanding. We present an approach that provides instructors in asynchronous and text-based computer-mediated communication settings with information about a learner's understanding that has sufficient diagnostic power to enable them to generate learner-tailored explanations. A series of experiments testing this approach suggest several conclusions. First, instructors need information about a learner to individualize explanations. Second, instructors are able to design explanations that are specifically adapted to a learner's individual understanding. Third, learner-tailored explanations facilitate the processing of new information and make instructional communication more efficient. Fourth, learner-tailored explanations enhance a deep understanding of the information processed and make instructional communication more effective.