[kiokusou]

I think you have to be prepared to explain the English, like all languages, is fluid. And far-reaching. Common usage in Australia is different to that in the States, or the UK.

[Eric18]

As previously noted and frequently overlooked, we need to recognize the limits of our knowledge and promptly apologize if we make errors.

When I first started teaching English to Russian immigrants, I would regularly have to say "let me double-check" on various grammar points. Students appreciated the honesty, but also felt that I should know the answer. They were right; I learned the material and became a better teacher. Despite a slow start, I earned their respect and they made "significant and meaningful progress."

A good lawyer avoids asking witnesses questions that she doesn't know the answers to. That same strategy in the classroom, however, limits student questions. Sometimes a student will ask us a question, inspired by but not directly linked to, the lessons and topics. Being open and honest means what it says. Sometimes, although you stand in front of the room, you will not know the answer. Just admit it, promise to find the answer to their good question, and keep your promise.

As the great philosopher Maimonides advised, "teach the tongue to say 'I don't know.' "

[Siddhartha]

Where the grammatical usage in textbooks is concerned, I think it also depends on where it was written, or rather, who wrote it.

I’ve certainly come across a number of textbooks written by non-native English speakers that promote language usage which would make any native speaker cringe. Even in such cases, I try not to come out and call it “wrong” but I do make it known that it’s not an example of usage that a native speaker would generally find acceptable.

Then there are textbooks written by native speakers of an English dialect which might make use of language in ways that seem strange or wrong according to your own dialect. Here, I think the best and most responsible thing to do is point out that there is a dialectal difference there, give examples of how the same thing might be expressed in your dialect (and any others you might be familiar with) and make sure they understand that each of these different ways of expression are equally valid.

[Eric18]

That's a smart, tactful, and effective technique. It's also an a reason to acquire better textbooks with more natural, authentic uses of English as spoken by native speakers in English speaking countries!

[Denis DNT]

Quote Eric18

.....of English as spoken by native speakers in English speaking countries!

Even that Eric, think of some of the forms native speakers employ when speaking. "We was..." "He don't...." etc.
Should forms like these be accepted for the simple fact that Native English speakers are using them or be corrected to follow standard English rules?