This is a late reply, but my school is ranked very low in nsw (around 400-500), and there are no special classes for the gifted and talented. But I can guarantee you that if youre doing well in a subject, and you show an interest in it your teachers will go above and beyond to help you out, give you resources, and improve your understanding of the subject.
In my case, my eng adv teacher is very generous in helping me out. I am doing well in english, yet the teacher understands that I enjoy and understand math + science better. She knows that my english writing can improve tremendously, and thus pushes me to do my best. She has purchased resources for me to be able to study and learn better, and has even offered to purchase textbooks and online subscriptions for me (I know, what an amazing teacher).
At the end of the day every school has teachers that want their students to do well. If you show an interest and appreciation in a subject, the teacher will go above and beyond in helping you regardless of there being a gifted and talented class - the teacher to an extent will treat you as an entire 'gifted and talented' class.