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What is Period of adolescent growth in boys is: and explain in detail?
Key Concept:
The stages of sexual development in boys are more difficult to specifically define than in girls. Puberty begins later and extends over a longer period-about 5 years compared with 3 1/2 years for girls.
Adolescent Growth Stages Versus Secondary Sexual Characteristics:
Girls:
Total Duration of Adolescent Growth: 3 ½  years 
Stage 1 
Beginning of adolescent growth 

Appearance of breast buds, initial pubic hair.

Stage 2 (About 12 months later)
Peak velocity in height 

Noticeable breast development, axillary hair, darker and more abundant pubic hair.

Stage 3 (12-18 months later)
Growth spurt ending

Menses, broadening of hips with adult fat distribution, breasts completed.

Boys:
Total Duration of Adolescent Growth: 5 years
Stage 1 
Beginning of adolescent growth

“Fat spurt” weight gain, feminine fat distribution.

Stage 2 (About 12 months later)
Height spurt beginning 

Redistribution and reduction in fat, pubic hair, growth of penis.

Stage 3 (8-12 months later)
Peak velocity in height 

Facial hair appears on upper lip only, axillary hair, muscular growth with harder, more angular body form.

Stage 4 (15-24 months later)
Growth spurt ending 

Facial hair on chin and lip, adult distribution and color of public and axillary hair, adult body form.

Ref: Contemporary orthodontics Proffit 6th ed  page 150