Early-life environment is strongly implicated in the development of social behavior across species, yet fundamental questions remain about the underlying behavioral mechanisms. We studied the mechanisms of early-life behavior development in the highly social African cichlid fish, Astatotilapia burtoni. By manipulating the number and concurrence of social partners during early-life, we were able to rear juveniles that varied in the quantity and quality of their social experiences. Fish were reared in a stable pair (one social partner); a rotating pair (novel social partner every five days, five total partners); or a stable group (five social partners). We then tested the effect of early-life social environment on individual social behavior in a battery of behavioral assays, including for dominant and subordinate behavior. We found that both the total number of social partners and group size influenced behavior. Fish from the rotating pairs were significantly more interactive than stable pair fish in both dominant and subordinate contexts. Group-reared fish initiated intermediate rates of behavior and were approached more by subordinates when dominant. The hypothalamic-pituitary-interrenal axis is a highly conserved mediator of early-life experiences, and in juvenile A. burtoni, rearing environment affects the neural expression of stress axis genes. Therefore, we quantified water-borne cortisol levels to investigate treatment differences and interactions with social behavior. These results provide insight into how the quality and quantity of social experiences during early-life shape behavior and underlying mechanisms.