But while the eight-year-old still has "years to wait until puberty, adolescence and finally sexual maturity ... a sort of lull before puberty arrives,'  with preadolescence proper (9–12), and the move forward from middle childhood, what have been called 'the introspective and social concerns of the prepubescent'  tend to come more to the fore. Clearly "few experiences are more prominent in the lives of preadolescents than the onset of puberty";  so that "at eleven or twelve you're just reaching the end of a long period during which change was steady and incremental":  Freud's latency years.
In females, changes in the primary sex characteristics involve growth of the uterus, vagina, and other aspects of the reproductive system. Menarche , the beginning of menstruation, is a relatively late development which follows a long series of hormonal changes.  Generally, a girl is not fully fertile until several years after menarche, as regular ovulation follows menarche by about two years.  Unlike males, therefore, females usually appear physically mature before they are capable of becoming pregnant.
Macintosh, K., & Dissanayake, C. (2006). Social skills and problem behaviours in school aged children with high-functioning autism and Asperger's disorder. Journal of Autism and Developmental Disorders, 36 , 1065-1076.
Despite the relatively few years separating one generation from the next, most adults seem to have amnesia about their own adolescence. Parents who have already "been there, done that" may have difficulty recalling how they felt and thought between the ages of twelve and twenty-one. As you read through the stages of adolescent development in this article series, try to recall what you were experiencing during those years. Whether your effort brings fond memories, a lot of pain or merely a sigh of relief that you don't have to go through that again, you will connect more smoothly with your teenager(s) if you can remember what it's like to walk a mile in their sneakers.