It is arguably teachers' most curious responsibility. For the past two decades, schools in England have had an official duty to nurture their pupils' "spiritual development".
It sounds a somewhat metaphysical challenge. Even if you can agree on what the word spiritual means, how on earth do you measure it? Yet it is there among Ofsted's criteria as something inspectors should evaluate in every school, as if it were as easy to gauge children's spirituality as it were to record their test scores and attendance rates.
If you ask teachers what their school does about pupils' spiritual development, some will shrug and mutter that they do a bit of stuff from the Bible in assembly. Headteachers of faith schools may start boasting about how their institution excels here because it is underpinned by strong faith values. But Ofsted states explicitly in its guidance that the word spiritual "is not synonymous with religious".
Atheist teachers should applaud the inspectorate for that. Religion does not deserve a monopoly over the spiritual, and in schools it should have a place in every subject instead of being treated as the preserve of the RE department.
Astronomer Carl Sagan described his awe at the universe and humanity's inventions as deeply spiritual. "Science is not only compatible with spirituality; it is a profound source of spirituality," he wrote.
This view is echoed by others, including John White, a professor at the University of London's Institute of Education. He defines pupils' spiritual development as relating to "the cosmic shudder we all feel from time to time when contemplating the existence of life, especially our own self-conscious life, and of the universe".
One of the clearest definitions comes not from a philosopher or a guru, but from Ofsted. It suggests that spiritual development means nurturing "that aspect of inner life through which pupils acquire insights into their personal existence which are of enduring worth".
If that is not a core purpose of teaching, it is hard to know what is. The duty to support pupils' spiritual development is not a curious responsibility, but the responsibility for their curiosity.
Michael Shaw is editor of TESpro firstname.lastname@example.org @mrmichaelshaw.