Just curious really? DS's new secondary school seems to be going with Before Christ and Anno Domini as the "house style" rather than Before Common Era and Common Era which slightly surprises me because they're normally quite modern in style and it has a significant Muslim minority.
What's the norm in British secondaries at the moment? Obviously you'd need to teach the DC to understand both formats anyway, because they'll see both in books and museums, but what would be the format expected in essays?