I remember correcting a student on Italki who wrote about a "door prize" which sounded very weird to me as it is not used in the UK and I was focused on the odd English of her text.  Recently, an American teacher here clearly told a student that "the family were" was wrong, without knowing that it is an acceptable option in UK English.  

People will make mistakes all their lives, and even be very sure that they are right.  By hanging around Italki forums long enough, teachers can pick up most of the common differences between US and UK English vocabulary, usage, and occasional grammatical issues. But I am sure I will keep seeing new things from time to time. 

Some people aren't even fully aware of how words are used in their own countries. More often than not, the supposedly "British" usage actually exists in the United States too, but is just less common, or is used regionally, or in a limited or technical way.

A device for passengers is always called an "elevator," but for freight both terms are used. As you can see, the Lightning Lift company of Delanco, New Jersey offers "freight lifts," "parking lifts," "subterranean car lifts," and so forth. 

http://www.lightningliftproducts.com/parking.html

And (of course?) in the United States, a "stairlift" is a motored seat that runs up a rail alongside a stairway, and is often installed in two-story houses to assist people who have trouble climbing stairs. A "chairlift" is piece of equipment that skiers use to ride to the top of a ski slope.

Lawrence touched on an interesting point.  Sometimes students want to know the answers to complex questions when they don't have the necessary experience to make sense of the answer.  Or they understand their own problems in terms which can't, of themselves, help them to overcome these problems.

I saw an Italki question recently to the effect of: I don't understand when to use "be" and when to use "have".  I can't imagine that a teacher would ever prepare a lesson (or package) focusing on the differences between those verbs.  For me, it would be nonsensical.  But it can be hard for students to grasp the next stages of their learning process and obviously there are always plenty of opinions and options.