In contrast to a large body of work concerning the effects of physiological stress reactivity on children’s socioemotional functioning, far less attention has been devoted to understanding the effects of such reactivity on cognitive, including mnemonic, functioning. How well children learn and remember information under stress has implications for a range of educational, clinical, and legal outcomes. We evaluated 8–14 year olds’ (N = 94, 50 female) memory for negative, neutral, and positive images. Youth had seen the images a week previously as a part of a laboratory stress task. At encoding and retrieval, and in between, youth provided saliva samples that were later assayed for cortisol, salivary α amylase (sAA), testosterone, and dehydroepiandrosterone (DHEA). Overall, higher cortisol reactivity to the lab task predicted enhanced memory for emotional but not neutral images. However, cortisol further interacted with pubertal hormones (testosterone and DHEA) to predict memory. Among girls with lower pubertal hormone levels, greater cortisol reactivity was associated with enhanced memory for negative information, whereas among boys with higher pubertal hormone levels, cortisol reactivity was associated with enhanced memory for positive information. sAA, was unrelated to memory. Overall, our findings reveal that individual differences in hormone levels associated with pubertal development have implications for our understanding of how stress-responsive biological systems directly and interactively influence cognitive outcomes.