The NSW OC and selective programs are purely based on academic TALENTED students. It assumes that talented students are also gifted. Of course, this is true 99% of the time. The selective tests are placed at the level way beyond normal ability where even a school teacher will fail to score well. The tests have a wide variety of questions across maths, English, general ability and a writing task. How can a kid who do well in this huge test over 3 hours could be without superior memory, mental processing, logical reasoning and vast amount of knowledge?
Still it is important to understand that not all gifted students become talented, and actually a big percentage of them won't. They just don't have the chances to develop their gifts. They may not be living in the right kind of family or community that value their gifts. They may not have the support to develop their gifts. They may have some learning disabilities that stop them from developing their gifts.
And more importantly, for those that already have parental support and good environment to develop their gifts, they should be parented well so they understand and embrace the development of their gifts rather than going for useless but extremely addictive stuff such as computer games, TV, YouTube, eating junk foods, online chat, ...
Another thing that people "know" but often "avoid" talking about in Western culture is the lack of the basics. Gifted kids are often lazy and ignore the learning of the basics. Because they are smart, their gifts actually mask the lack of basics. They can score well by guessing the multiple choice questions or even come up with the right short answers without actually understand it. Therefore it is really harmful to think of gifted education as different than normal education. It is more useful to think about gifted education as cutting back on normal education (while still keeping the core), and add a lot of advanced and challenging stuff to fit the needs of gifted kids. Taking the basics and help the kids to understand deeper is also part of education for the gifted kids. This is what many tend to overlook! The result is a poorly formed foundation and that is bad for their future learning at higher levels. So a lot just stop being talented when they get to higher years.