Normal Adolescent Growth, Development, and Puberty
The pubertal engine
Puberty begins when the hypothalamic GnRH pulse generator reawakens after a decade of quiescence, driving LH/FSH pulses that mature the gonads (gonadarche). Adrenal androgens rise separately (adrenarche) and may produce pubic and axillary hair before gonadarche. Keep these two systems distinct: isolated pubic hair with no breast budding or testicular growth is premature adrenarche, not precocious puberty, and usually needs only observation.
Tanner staging and the sequence
In girls, thelarche (breast bud, B2) is the first sign at an average of 9-11 years; pubic hair follows; peak height velocity (~9 cm/year) occurs around B3-B4, roughly a year after thelarche; menarche arrives about 2-2.5 years after thelarche (average 12.5 years) and signals decelerating growth, not its onset. In boys, testicular volume of 4 mL or more (G2) is the first sign at about 11.5 years; the growth spurt comes later (peak ~10.3 cm/year at G4), which is why boys grow longer and end taller. Gynecomastia peaks at G3-G4 and usually resolves within 1-2 years.
What goes wrong
Precocious puberty means any secondary sexual characteristic before 8 years in girls or 9 in boys. In boys it is almost always gonadotropin-dependent, so image the brain; in girls most cases are idiopathic. Delayed puberty means no breast budding by 13, no menarche by 15 (or more than 3 years after thelarche), or no testicular enlargement by 14. Compare bone age to chronologic age: constitutional delay shows a delayed bone age with predicted adult height in the normal range, whereas familial short stature shows a normal bone age tracking the mid-parental target.
Rule of thumb
Mid-parental height = (mother's height + father's height)/2, plus 6.5 cm for boys, minus 6.5 cm for girls. Calculate it before declaring anyone too short.