A wealth of human knowledge is acquired by attending to information provided by other people--but some people are more credible sources than others. In two experiments, we explored whether young children spontaneously keep track of an individual's history of being accurate or inaccurate and use this information to facilitate subsequent learning. We found that 3- and 4-year-olds favor a previously accurate individual when learning new words and learning new object functions and applied the principle of mutual exclusivity to the newly learned words but not the newly learned functions. These findings expand upon previous research in a number of ways, most importantly by showing that (a) children spontaneously keep track of an individual's history and use it to guide subsequent learning without any prompting, and (b) children's sensitivity to others' prior accuracy is not specific to the domain of language.