What's the difference between 我是老师 or 我当老师?

Question

Sometimes when I take a 滴滴打车 taxi to the university campus, the driver asks me if I'm a student, and I reply something along the lines of:

我是老师
I'm a teacher
_{Wǒ shì lǎoshī}

As far as I can tell, this is grammatically correct. However, more than once, the driver replied:

你当老师
You're a teacher
_{Nǐ dāng lǎoshī}

It feels almost like they're correcting me, but I don't really understand why. It's possible 我是老师 sounds more along the lines of what a child might say as it's very simple. (It's also possible I simply misheard them.)

Question: What's the difference between 我是老师 or 我当老师?

Among the zillions of meanings of 当, one is "to act as", so maybe 我当老师 has a meaning closer to "I perform the role of a teacher". But I still see no concrete reason that 我是老师 is wrong or inferior.

Answer 1

我是老师 = I am a teacher" It is completely correct

当 is a verb that means 'to be/ working as/ take on the role or position of'

你当老师= you being a teacher

你来当老师 = you'll be a teacher

你去当老师 = you go and be a teacher

你当上了老师 = you've became a teacher

The driver's question "你当老师?" (you being a teacher?) was a rhetorical one. That imply "It is hard to believe people as young as you would be a teacher." He could had asked "你是老师?" and the meaning would be the same.