Perseverance, above and beyond IQ, predicts academic outcomes in school age children. Yet, little is known about how very young children learn the contexts in which persistence is valuable (or not). Here, we explore how young children and infants learn about the rational deployment of effort through observing adults’ persistent behavior. Results from Experiments 1 and 2 indicate that preschoolers persist more after watching an adult persist, but only if the adult is successful at reaching their goal. Experiment 3 extends these findings, showing that even infants use adult models to modulate their persistence, and can generalize this inference to novel situations. Thus, both preschoolers and infants are sensitive to adult persistence and use it to calibrate their own tenacity.