The best answer to that question is a question. What were the principles that the framers of the Constituion used to design the foundation of the United States? Why did they think religious freedom was so important that it required its own amendment?

I pose the two questions to provoke thought as to how the mores of this coutry have changed over time.  The case of Engel v. Vitale, 82 S. Ct. 1261 (1962) dictated that any kind of prayer, composed by public school districts, even nondenominational prayer, is unconstitutional government sponsorship of religion. This among other rulings took away a child's abilty to openly pray as a group in a public school enviroment.  Please note that the judgements and established laws do not discrminate with regard to the religion being practiced.

Simply, I believe there is a reason and cause for prayer  to be an acceptable practice in any school that chosses to adopt it. A child and his/her parent still has the right to participate in the activity.