I don't know whether it's grammatically correct to say, "I have 9 scissors" instead of, "I have 9 pairs of scissors". I couldn't find a grammar rule that would back it up, but I didn't search for a super long time either.
I'm pretty sure what you'll find though is this: that it's grammatically correct to use the word, "pair(s)" when you are speaking about a specific number, but in reality, a lot of people omit it. The omission probably happens frequently enough in native English speakers' speech to say it's colloquial English - at least in America. (I'm sure they never say it that way in England.)
That being said, when we are talking about only 1 pair, "a pair of scissors" or "some scissors" is most common.
I teach the word "pair" but don't worry too much about corrections unless I'm teaching partitives/collective nouns. But I guess that's up to you and your co-teacher.
Hope that helps.