"Our school has around a thousand students."
Translation:Nuestra escuela tiene alrededor de mil estudiantes.
The 'de' here does not mean 'a'. It goes with alrededor and it is a two word adverb in Spanish meaning (aproximadamente or about). http://www.spanishdict.com/translate/alrededor%20de
alrededor means around as in mirar alrededor (to look around).
Alrededor is also a masculine noun as in miré a mi alrededor I looked around me as in surroundings,
I have found that very often the English meaning will not always translate exactly to Spanish and the reverse.
I think that the word that you are looking for is "cerca".
It could work, but I think that, in this context, these words encompass different ranges of numbers. If you use "cerca", it means that the school has less than a thousand students. On the other hand, if you use "alrededor", it means that the school may have either more than a thousand students, or less than that.
EDIT: Mavry is right, you can use them interchangeably here, I'm just being picky (:
The problem is when i research the two words the dictionary gives 'alrededor de' as an adverb, but cerca de as a preposition. I really am confused because to me cerca de would mean near by, or close to, or even about.
As a non native speaker, things like this confuse me. Your input is welcome as well as Mavry, as he has been helping us English speakers out around these discussion sentences for two or three years now.