When looking at gender differences in development it can be difficult to tell if those differences are from biology or from social pressure. In an effort to remove the nature vs. nurture factor some researchers look at the development of children under the age of two, reasoning they are too young to be influence by society's preconceptions of gender roles. What they've found is that there isn't much difference between baby boys and girls.
In a 2006 study published in "Acta Pediatrica," researchers at the World Health Organization published the results of their Multicentre Growth Reference Study, which looked at child development across cultures. They compared six gross motor skill milestones, of sitting without support, crawling, standing with assistance, walking with assistance, standing alone, and walking alone, and assessed these longitudinally in five of the six sites in the study. They followed children in Ghana, India, Norway, Oman and in the U.S. from 4 months to 24 months. The researchers concluded that the study demonstrated no significant developmental differences between boys and girls.
A study done by David S. Moore, professor of psychology at Pitzer College and Claremont Graduate University, both of Claremont, California, demonstrated that 5-month-old boys were better able to mentally rotate complex objects than were 5-month-old girls. Mental rotation refers to the ability to mentally rotate representations two and three-dimensional objects, and to determine similarities and differences between the two. An article on "Cognitive Gender Differences" by Abigail James on Education.com noted similar results, but also cited research that showed infant girls were better at perceptual speed than boys of the same age. Perceptual speed is a skill that involves matching objects and pictures and so on. Both articles pointed out that these differences disappear as the child grows older. It appears that boys and girls may develop skills in a different order but overall at the same speed.
A September 2009 article, "Girl Brain, Boy Brain?" by Lise Eliot in "Scientific American," pointed out that girls show more empathy than boys as early as infancy and, unlike cognitive skills, the gap grows as the children age into adulthood. The author postulated that the early difference is due to hormonal or genetic influence but the later changes are due to social expectations regarding male and female gender roles. If true, this shows how both nature and nurture are important driving factors for gender differences in development.
One factor that clouds the gender difference issue is individual perception. One 2000 study, the "Gender Bias in Mothers’ Expectations about Infant Crawling," published in the "Journal of Experimental Child Psychology," examined 11-month-old babies and found no differences in their ability to crawl. However, the mothers of the infants tended to overestimate how well the boys crawled and to underestimate the performance of the girls. An article in the January 2006 issue of the journal, "Sex Roles," showed mothers engaged in different speech and play behavior with their infants, depending on whether the child was male or female.