The biological phenomenon that girls tend to experience their main growth phase earlier than boys is a universally observed pattern tied directly to the onset of puberty. This difference in timing explains why girls are often taller than boys for a brief period during middle school years. The acceleration of growth is driven by the activation of the endocrine system, which releases sex-specific hormones into the body. Examining these mechanisms reveals the distinct hormonal pathways that produce these contrasting developmental timelines.
The Timing of Growth Spurts
The adolescent growth spurt represents the most intense period of growth after infancy, and its timing is consistently earlier in girls than in boys. This phase is clinically measured by Peak Height Velocity (PHV), which marks the fastest rate of height increase an individual achieves. On average, girls reach their PHV around 11 to 12 years of age, while boys typically reach theirs about two years later, around 13 to 14 years old.
The earlier start means girls begin their rapid acceleration of growth approximately 1.5 to 2 years before their male peers. Because of this head start, girls in their pre-teen and early teen years are temporarily taller and have a more advanced level of skeletal maturity. The overall magnitude of the spurt differs as well; girls achieve a PHV of approximately 9.8 cm per year, while boys experience a slightly greater magnitude, reaching an average PHV of 11.3 cm per year.
Estrogen and Testosterone as Growth Accelerators
The distinct timing and magnitude of the growth spurt are regulated by the differential release and action of sex hormones, specifically estrogen and testosterone. The pubertal growth phase is initiated by a rise in Growth Hormone (GH) and Insulin-like Growth Factor-1 (IGF-1), but sex hormones modulate their effectiveness. Estrogen is considered the main hormone responsible for stimulating the pubertal growth spurt in both sexes, influencing linear bone growth both directly at the growth plate and indirectly by stimulating GH secretion.
In girls, the body begins secreting increasing levels of estrogen (estradiol) at the onset of puberty, which triggers the early and rapid acceleration of growth. This early estrogen exposure drives bone development at a faster pace, leading to the earlier PHV observed in females. The concerted action of estrogen, GH, and androstenedione drives the female growth trajectory.
In boys, the pubertal growth spurt is driven primarily by a significant increase in testosterone, which also stimulates the release of GH and IGF-1. Much of the growth-promoting effect of testosterone is due to its conversion into estrogen within the bone and other tissues, a process called aromatization. Testosterone also has a direct effect on the growth plate, increasing the local production of IGF-1. This later surge of testosterone allows the growth period to be sustained for a longer duration, contributing to the greater overall growth magnitude seen in boys.
Skeletal Maturation and Growth Cessation
The reason girls grow faster initially but boys ultimately grow taller on average lies in the process of skeletal maturation and the permanent cessation of growth. Long bones lengthen at the epiphyseal plates, or growth plates, which are zones of cartilage found near the ends of bones. When the cartilage cells in these plates stop multiplying and are completely replaced by solid bone, the growth plate fuses or closes, and no further height gain is possible.
Estrogen is the primary biological signal that drives the fusion of these growth plates in both males and females. Because girls experience an earlier and more pronounced rise in estrogen concentration, their growth plates begin the process of closing sooner. This leads to an earlier end to the growth phase, typically between 13 and 15 years of age.
Boys experience their testosterone surge later. While this hormone is ultimately converted to estrogen to facilitate growth and closure, the process takes longer. The delay in the estrogen-driven fusion signal allows boys’ long bones to continue lengthening for an extended period. Consequently, the growth plates in males close later, often between the ages of 15 and 17, giving them an extra two to three years of growth that results in a greater average final height.