19 juvenile members of known genealogies in two wild baboon groups were studied over a 16-month period. Males and females in two age classes were compared regarding third-party aggression and support given and received during agonistic interaction. Young juvenile males and females (1–2.5 years-old) were supported predominantly by their probable fathers. The adult males supported without regard to the family ranks of juveniles and their opponents. Old juveniles (3–5.5 years-old) no longer had probable fathers in their groups and rarely or never received support from adult males. Females received considerable maternal support and, with age, most often received support from unrelated adult females. Males rarely received support from either their mothers or unrelated adult females. 100% of adult female support for and against 11 of the 12 females reinforced existing rank relations among matrilines. In contrast, only about half of adult female support of males reinforced matrilineal rank relations. Juvenile females exploited aggression among adult females during rank acquisition: they supported high-ranking adults during attacks on females they had targeted for rank reversal. In contrast, males attacked adult females in support of peers or young juveniles. Females also solicited support during fights more often than males. They most often solicited adult females, whereas males directed their rare solicitations toward other males. Despite low maternal rank, one female targeted all older females for rank reversal except the adults of her group's top-ranking family. She was the only female to receive support from adult females that contradicted existing rank relations among matrilines, and the only female ultimately to achieve stable adult rank above families outranking her own. Adult female baboons appear to structure the development of rank relations for juveniles in their groups. Juvenile females are typically limited to acquisition of familial status, while males are free to achieve rank over whichever group members they can independently intimidate.