I'd have to disagree that it's straightforward. Gentrification and pockets of higher income areas do exist within many lower decile schools' catchment areas (Wattle Downs near James Cook). And the students who go further afield are not likely to be in their new school's majority.

While decile rating is linked to students, it isn't straightforward that students avoiding their local lower-decile school will cause the school they end up at to decline in decile.

As noted by principals in the article, they will tend to be from higher income families within an area, and in many cases their household incomes etc will not be typical of others at the local low-decile school - so when they end up at a higher decile school further away their family backgrounds may not be as different as their peers who live closer by. And if they end up at a school of reasonable size then their impact might not be great enough to bring the decile down, it's unlikely they will be in the majority.

Further complicating the picture is the fact it can be years and years between decile recalculations, and that they are worked out nationally.