It should be noted too that girls have more white matter (over 9.5 times more than boys), the neurological wiring, that connects various parts of the brain. Plus, sex hormones play a key role in brain development. Girls do have such exposure to testosterone levels as boys.

Even with 2- and three-year-old girls and boys at a playground, you might notice the girls, generally speaking, seem to be more purposeful with their play. Boys (generally speaking), on the other hand, can be totally aimless and run around without any goal or plan in mind. They're wired differently.