When are girls expected to start there period? Just woderin

Menarche is another name for the beginning of menstruation. In the United States, the average age a girl starts menstruating is 12. However, this does not mean that all girls start at the same age. A girl can begin menstruating anytime between the ages of 8 and 16. Menstruation will not occur until all parts of a girl's reproductive system have matured and are working together.

For further information, you can read through:

Menstruation - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Menstruation)