Why is it that women pray behind men?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
As for women praying behind men, there is no doubt it is more appropriate to screen them and protect them from any embarrassment. Can you imagine the distraction to men being in rows behind women and following their Ruku and Sujud ?. Any person who looks attentively at the Shari'a finds that it is best and wise in dealing with all issues and particularly this noble ritual of Islam which requires the person to be humble, patient and concentrating to avoid any distraction during this great form of Ibadah (worship).

Allah knows best.