I guess it depends on where you are teaching, I mean you may have to consider the historical background and the practicality of the language in that place. For example, in Japan and the Philippines, American English may be preferred and in India British Engish may be preferred.
Just a personal experience:
I live in Hong Kong and Hong Kong was ruled by the British, so British English has been preferred in our education system. But in reality American English is everywhere, on TV and movies, in newspapers and magazine. So from time to time, teachers need to point out the difference between British English and American English. In a way, I think I was learning both.
When I was a student, I always thought American English sounded more 'stylish' and 'fashioable' because most TV stars and movie stars speak American English .
I am no longer a student now. I work and I find that understanding both helps my work because the people that we work with include both British and Americans. So it might have caused communication problems if I knew only either of them.
I guess HK is knid of 'international', so learning both is useful. But in some places, learning only one of them is enough.