Physical Development in Boys

Puberty can be a scary time for boys and their parents. Many parents aren't sure how to explain the changes taking place in their children's bodies, while many kids are afraid to ask too many questions. Many boys may worry that they are not developing normally, but honest conversations between kids, parents and their doctors can put most of these fears to rest. Physical development happens in stages, often described as the Tanner Stages, a system of classifying pubertal development developed by Professor James M. Tanner.

Tanner Stage 1

Tanner Stage 1 simply describes a child who has not yet reached puberty. There will be no body hair changes and no changes in the size of the penis and testes. Children still in Tanner Stage 1 will generally grow at an average rate of approximately 2 inches a year.

Tanner Stage 2

Children can reach Tanner Stage 2 somewhere between the ages of 9 1/2 and 14 1/2 years old. Height will continue at an average rate of approximately 2 inches a year, but kids reaching Tanner Stage 2 will now begin to notice growth of the testes somewhere around the age of 11 1/2 years old. Scrotum and testes growth is one of the first signs of puberty and will be accompanied by tiny bumps of developing hair follicles. Boys will also notice a slight growth in penis size at the same time, followed by minimal pubic hair growth around the age of 12.

Tanner Stage 3

Between the ages of 11 1/2 and 16 1/2 years old, boys will enter Tanner Stage 3. Their rate of height will increase to approximately 2 3/4 to 3 inches a year, and they will experience increased growth in other areas as well. Testes will more than double in size at this point, around the age of 14. The penis will continue to grow, first in length and then in width. Pubic hair will increase and continue to grow over the pubis around age 13. Boys in Tanner Stage 3 will also begin to develop breaks in their voice as their larynx and vocal cords increase in size and their voice begins to change to a lower register.

Tanner Stage 4

Boys reaching Tanner Stage 4 begin their maximal growth spurt, shooting up at a rate of approximately 4 inches a year. Pubic hair begins to develop an adult texture and quality, but has not spread to an adult distribution just yet. Testes grow at a slower rate, but the penis continues to grow in both length and width. Boys will develop underarm hair at this stage, around age 14, and will continue to experience voice change side effects. Acne is also a common physical development around age 14 2.

Tanner Stage 5

Tanner Stage 5 marks the end of puberty, somewhere around the age of 17 for most boys. The penis will reach it's final size around the age of 16 1/2, and the testes will reach their final size as well. Boys will also be finished growing in height by about the age of 17. Pubic hair may reach its final adult distribution even earlier, covering the entire pubis and spreading to the medial thigh. Boys will have developed facial hair and a more muscular physique by the end of Tanner Stage 5. Many boys are concerned about penis size, but most fall within the range of normal and may be reassured by their doctor if they have questions.


Boys have erections and can experience pleasurable sensations from their penis since infancy, but are not fertile or able to ejaculate until they reach spermarche, usually around a year after their testicles begin to enlarge. Boys may be embarrassed by frequent uncontrollable erections and by nocturnal emissions, ejaculation that occurs while they are sleeping, but try to assure kids that this is entirely normal and happening to all of their friends as well.

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