This study interconnects developmental psychology of fair and moral behavior with economic game theory. One hundred eighty-nine 9- to 17-year-old students shared a sum of money as individuals and groups with another anonymous group (dictator game). Individual allocations did not differ by age but did by gender and were predicted by participants' preferences for fair allocations. Group decision making followed a majority process. Level of moral reasoning did not predict individual offers, but group members with a higher moral reasoning ability were more influential during group negotiations and in influencing group outcomes. The youngest participants justified offers more frequently by referring to simple distribution principles. Older participants employed more complex reasons to justify deviations from allocation principles.