That is clearly wrong, a violation of the separation of government and religion. But I've heard about student-initiated prayer, where the students want to pray. Student populations often reflect the diversity of the culture. Lately, there have been court cases involving this very question. Our society, though, is one where most people are religious, and believers in Christianity.
Religion plays only a minor role in their lives, if at all.
And consider the believers. They are fragmented into thousands of sects, denominations and different persuasions. They cannot agree on which holy book to use, which god to worship or which prayer to use. School prayer boosters have sometimes proposed this as a way of establishing a legal precedent which, they hope, will eventually lead toward explicit and vocal school prayer. Besides, consider the declining number of hours that students are in school each year.