In boys-cracking of voice, shoulders broadens, growing hairs on armpits,chest and genitals, growing facial hair,    in girls-thigh and hips broadens, growing hairs on armpits and genitals,size of breast increases due to mammary gland
Secondary sexual characteristics :
In male :
1. the voice changes, become deeper.
2. development of muscle tissue and a growth spurt.
3. growth of body hair - pubic, chest and face.

In female :
1. change in body shape, rounder hips.
2. development to mammary glands.
3. growth of pubic hair.
4. increase in fat tissue; essential for fertility.

As a general rule males are taller and heavier than females.