School officials in California are fighting a lawsuit brought by a conservative organisation on behalf of a group of Christian parents to prevent the district from teaching primary school children yoga, which they claim is a form of indoctrination.

It is a case that brings together some of the most combustible ingredients in American public life - schools, religion and the First Amendment, which enshrines freedom of religion and separates church and state - and is being closely watched by public institutions throughout the country that have begun to teach or allow the practice of Ashtanga yoga.

Classroom peace: First-grader Miriam Ruiz practises her yoga at a school in Encinitas, California. Credit:The New York Times

The dispute began late last year, when the Encinitas public school district in San Diego introduced yoga as part of its mandated physical education curriculum.

Though many schools in the US have taught yoga, it is thought this is the first district to formalise it across the board. Apparently aware of the potential for controversy, the district stripped from the course the traditional chants and Sanskrit words associated with the practice, and provided alternatives to children whose parents chose to opt out.