The head of a Christian schools group has defended the practice of having students sing an additional religious verse to the national anthem.

Instead of the official second verse of Advance Australia Fair, the alternative verse reads:

With Christ our head and cornerstone, we'll build our nation's might; Whose way and truth and light alone, can guide our path aright; Our lives a sacrifice of love, reflect our master's care; With faces turned to heav'n above, Advance Australia Fair; In joyful strains then let us sing, Advance Australia Fair.

It has been reported that students at at least two private schools in Perth sing the extra verse.

Christian Schools Australia chief executive Stephen O'Doherty told the ABC there is nothing wrong with singing an additional verse.

"What sort of nation is it if somebody wants to stop young kids from singing that they want to be servants of their nation; they want to build community on the strong foundations of their belief in God?"

But Warren Pearson, chief executive of the National Australia Day Council, says changing the words should not be encouraged because students are no longer singing the national anthem.

"I think it's wonderful that young people in Christian schools, in all different schools, sing the national anthem," he said.

"And in some schools they might go and sing the Christian verse, that's fine, but at that point they are singing the verse from Advance Australia Fair; technically they're no longer singing the national anthem."