They develop at different rates: right hemisphere develops more rapidly in the first few years of life, and then the left hemisphere becomes more dominant in terms of development. (Siegel, Daniel J., MD. The Developing Mind. NY: The Guilford Press, 1999, pp 193-194)

The right hemisphere has relatively more white (myelinated) matter, while the left has more gray. The axons in the right brain are longer than in the left and connect neurons that are, on average, further away from one another. (Carter, Rita, Ed. Mapping the Mind. CA: University of California Press, 1998, p 38)