Now, this took some getting used to when I first started
teaching in South Africa, where they use the same system. Why?
Because when/where I was a child, a checkmark (AmE for ✓) on
your work meant that you got it wrong. This is actually fairly
counterintuitive, because a ✓ can mean 'good' in various other
contexts. For instance, if I wrote an essay in school and it was
just OK, it would get a ✓ at the top of the page. If it were
(usual BrE = was--but we'll get to the subjunctive some other
time) very good, it would receive a ✓+ or ✓++. And a ✓ in an
advertisement or on a grocery list means 'we've got it' or
'mission accomplished' or similarly positive things. It seems
that many American schools use the British system of ✓ for
'correct' and X for 'incorrect', while calling them check(mark)s
and exes still. It's not clear to me whether this is a recent
innovation or a long-standing variation. (American readers--did
you get checked or exed wrong, and when?) But there is some
evidence that the system that I knew