The development of fairness considerations in decision making is not well understood. Here we tested the hypothesis that increased understanding of intentionality during adolescence underlies increased fairness considerations in social decision making. We conducted three experiments using an adapted version of the Ultimatum Game with participants during four stages of adolescence: 9, 12, 15, and 18 years of age. Participants made or evaluated monetary offers, and we manipulated the intentionality context of offers. Results show that strategic thinking is already present at 9 years of age. There was no age difference in fairness of offers when the responder could not reject an offer (Experiment 1), but when they could reject an offer there was an age-related increase in taking into account the perspective and intentionality of other players when making offers (Experiment 2) and evaluating offers (Experiment 3). Taken together, the results demonstrate a linear developmental transition in fairness considerations that may have important implications for our understanding of social interactions during adolescence.