Pubertal development is regulated by the hypothalamic-pituitary-gonadal (HPG) axis. Tanner staging ranges from 1 through 5 (with 5 being the most developed).With regards to pubic hair development, the scale goes as follows: Stage 1-no hair; 2-downy hair; 3-scant terminal hair; 4-terminal hair overlying the pubic triangle; 5-terminal hair extending to the thigh. With regards to male genitalia development, the scale goes as follows: 1-testes at the same size and proportion of early childhood; 2-enlargement of the scrotum/change in texture of scrotal skin; 3-growth of the penis length-wise; 4-growth of the penis in terms of length and circumference; 5-adult-sized genitalia. With regards to female breast development, the scale is as follows: 1-no palpable gland tissue; 2-palpable breast bud under areola; 3-breast tissue palpable outside of areola; 4-areola elevated above breast contour; 5-areolar mound recedes into single breast contour. The average age in which both males and females reach Tanner stage 5 of pubertal development is around 15–16. Neurological development
There are significant neurological changes that are expressed during preadolescence. White matter refers to the region of the nervous system corresponding to neuronal axons, which form fibers that convey information across different regions of the brain. In contrast, grey matter refers to the region of the nervous system corresponding to neuronal cell bodies, which process and relay neuronal signals. White matter volume increases at a relatively linear rate of about 12% from ages 4 through 22, specifically focused in the frontal, parietal, and occipital lobes.
Middle children generally show more investment in control over external reality through the acquisition of knowledge and competence: where they do have worries, these may be more a fear of kidnappings, rapes, and scary media events, as opposed to fantasy things (e.g., witches, monsters, ghosts). Preadolescents may well view human relationships differently (e.g. they may notice the flawed, human side of authority figures). Alongside that, they may begin to develop a sense of self-identity, and to have increased feelings of independence: may feel an individual, no longer "just one of the family." A different view on morality can emerge; and the middle child will also show more cooperativeness. The ability to balance ones own needs with those of others in group activities. Many preadolescents will often start to question their home life and surroundings around this time and they may also start to form opinions that may differ from their upbringing in regards to issues such as politics, religion, sexuality, and gender roles. Greater responsibility within the family can also appear, as middle children become responsible for younger siblings and relatives, as with babysitting; while preadolescents may start caring about what they look like and what they are wearing. Prior to adolescence, children may have a dependence on their family as their main agent of socialization. This helps the child establish their attitudes, viewpoints, social norms, and societal roles.Among these changes is the shift from elementary to middle (or junior high) school.