In the current study, we attempted to highlight one such ability required for high-quality instruction: the ability to track what learners understand (e.g., Kruger & Tomasello, 1996; Wood, Wood, Ainsworth, & O’Malley, 1995). One method for evaluating a learner’s knowledge is to analyze the learner’s specific mistakes, allowing for specialized instruction explicitly targeting areas of confusion. Thus, the first goal of our study was to examine the development of children’s ability to infer how much someone knows based on his or her mistakes.