Moving house is an option, but different parents weigh it differently, given the scarcity of superselective grammar, most who get in have to move or travel long distances.
You must be joking, surely. So a family with a bright child who lives on a farm (ie not a portable job) on the Isle of Wight should move to an area with super selective grammar schools, regardless of the needs of any others in the family?
Like most of those outside of these strange little elite locations, I had never heard of such schools. They could never open in areas like Cornwall or the IoW or North Wales because they are not economically viable or logistically feasible.
Our exceptionally bright children perform equally well as those hot housed and haven't been wrapped up in cotton wool in case they catch the ick from those who are less academic. Non-selective schools differentiate - my daughter didn't do the same work as those in her class aiming for 2s or 3s but they worked alongside each other well.
There are disruptive children in every school. Simply being entered for and passing an exam when you are 10 or 11 doesn't reduce the risk of doing drugs, having MH problems etc.