Although the functionalist perspective on emotional development posits that emotions serve adaptive functions, empirical tests of the role of anger mostly focus on how anger contributes to dysfunction. Developmentally, as children gain agency and skill at emotion regulation between the ages of 36 months and 48 months, their modulation of anger may facilitate its functional role for behavior. We examined this possibility through study of how 120 children's anger and sadness were related to persistence during the transparent locked box task at ages 36 and 48 months. Using survival analyses, we examined how children's anger and sadness were related to their giving up during the challenging task, and whether those relations were moderated by age. Using hidden Markov models (HMMs), we examined how children transitioned among anger, sadness, and on-task behavior states and whether those dynamics differed with age. Survival analysis revealed that age moderated the relation between anger and giving up. Greater anger was associated with greater likelihood of giving up earlier in the task at 36 months but with lower likelihood of giving up at 48 months. HMM analyses revealed that children were more likely to transition from a Calm/On-task to Calm/Off-task state at 36 months than at 48 months; that children were more likely to remain in an Anger/On-task state at 36 months than at 48 months; and that children were more likely to transition from Calm/On-task to Anger/On-task, and from Anger/On-task back to Calm/On-task at 48 months than at 36 months. Taken together, the findings suggest that anger appraisals may facilitate children in maintaining persistence, but that this functionality may develop with age.