In an article on Male Puberty, they say that "Stage four of male puberty commonly takes place when a boy is around 14 or 15 years old. Hair begins showing up in the armpits and on the face, and pubic hair begins to grow coarse. The boy's voice will even out and become deeper. The stage-four boy can use this deeper voice to yell forcefully at the mirror when he sees his new acne, due to his ever-more-oily skin. He begins to grow taller and even faster, at about 4 inches (10.2 centimeters) a year. The penis now grows thicker and continues to lengthen." Is this true?
It also says that a boy may grow 12inches (1ft) during puberty. How many inches in stage 2?
Dr. Tanner divided adolescents into five stages:
- Childhood, pre-puberty
- Initial puberty
- Increasing growth rate
- Decreasing growth rate
- Adulthood, growth in height stops
He was interested in quantifying secondary signs to give physicians clues as to which stage an adolescent was in. For boys he used pubic hair and genital development as the clues. Others since him expanded the clues to other areas.
One of the difficulties is the transition from stage 3 to stage 4. Do you put the peak on the stage 3 side or the stage 4 side? Dr. Tanner put the peak on the stage 4 side, even though it didn't last long. The problem I noted was that it makes stage 3 short and stage 4 long. Others put the peak at the transition point or at the end of stage 3. But with girls, Dr. Tanner used a different division, putting the transition a bit later -- when the growth rate returns to a childhood level of about two inches per year. He appears to have done this to make the divisions between stages based on secondary signs clearer to distinguish. I found division at the return to childhood growth levels particularly appealing because it makes the length of stage 3 and stage 4 more equal. Instead of using a different definition for boys and girls, I decided to use one that was consistent between both sexes. This is the definition I use in the calculator.
The article you cited uses the definition where the peak is at the start of stage 4. However, the author didn't catch that it is slowing down during stage 4. Because of this small error, he also concluded that there is continued growth in height after stage 5 (thus creating six stages).
The author also makes it appear that the rate of growth is consistent between males -- it is not. Peak growth rates can be anywhere from 3 to 8 inches per year.
He also doesn't make it clear that age and stages are not tightly coupled. They are only loosely coupled. For example puberty (stage 2) can start as early as 9 or as late as 16 in males and be considered normal.
It isn't that the article is bad. It just isn't as precise as I like to present information.
Stage 2 continues the rate of growth in childhood, which is usually 1 to 2 inches per year. Since stage 2 lasts roughly two years, it means you grow 2 to 4 inches during stage 2.