At which Tanner stage does the onset of puberty begin?

Puberty is a developmental stage marked by various physical changes, and Tanner stages are used to classify these changes in children and adolescents. The onset of puberty typically begins at Tanner Stage II.

At Tanner Stage II for both boys and girls, initial signs of puberty are seen. For girls, this includes the development of breast buds, which signifies the onset of breast development. In boys, there is an increase in testicular size as well as some hair growth in the pubic area. These developments are key indicators that hormonal changes associated with puberty are starting to take place.

Tanner Stage I is characterized by prepubescent physical development, where there are no significant signs of sexual maturation. Tanner Stages III and IV reflect further progression in physical development beyond the initial changes seen in Stage II, including more advanced breast development in girls and increased size and pubic hair changes in boys. Thus, the correct choice is Tanner Stage II, as it represents the very beginning of physical changes associated with puberty.