These years, sometimes referred to as adolescence, are often the most chaotic and turbulent of a person's life as they are a time of extreme changes, physically, mentally, and emotionally. The age at which youngsters reach puberty varies, of course, by individual, with girls tending to begin the physical developments sooner than boys, but generally speaking, adolescence and the onset of puberty are thought to begin as early as age ten, and sometimes as late as thirteen or fourteen. These transitional years mark the beginning of physical changes that will result in reproductive capacities as adults, of course, and this is also the time when children, in their roles as students, begin to worry less about pleasing the adults around them and much more about pleasing, and fitting in, with their peers. This can be quite a challenge for teachers of fifth and sixth graders, for example, as the tendency in some schools is to treat those kids the same as children in the primary grades, who are often very eager to please their teachers. As the child enters seventh and eight grades (although sometimes earlier) the need to please the peer group and fit in may lead to situations involving drinking, drugs and/or sex that the child is not ready to handle.
Although high school can be difficult for many kids as well, some kids begin to thrive in the environment where many different activities are offered and they can more easily find a place to fit in and the role of cliques, if not completely eradicated, is in some cases minimized (whereas in middle school, one is generally in the "in" crowd, or is not). However, there are those whose difficulties growing up may continue on into the high school years, particularly if a youngster has no support at home when things get tough. These, of course, are the kids everyone worries about, because they tend sometimes to gravitate to the "wrong" crowd searching for acceptance and belonging.
Interestingly, one's development into adulthood may not end as early as previously thought. Research has confirmed that brain development is not completed until the early twenties; of course, the ramifications of this can be deadly. Occasionally, one hears about a tragic accident involving kids in their late teens or early twenties that may have been caused by poor decisions likely influenced by an inability to contemplate or foresee dangerous consequences. In other words, kids often hear their parents' warnings about danger, and intellectually understand them, but don't heed those warnings because they quite literally can't fathom a dangerous outcome; the part of their bring that would predict dire consequences is not developed yet.