As a retired grammar school headteacher who took his school through the same process some years ago, I am well aware of the uncertainties, especially around funding for the required building extensions. If the relevant approvals are forthcoming, and there is clearly a strong case for this to happen, there will need to be a double entry age for September 2016 and 2017 at eleven and thirteen, so that no children are disadvantaged and the school can operate as a fully 11-18 school from September 2018.
As explained in my article this is going to have a considerable effect on admission patterns, as at present a high proportion of the day intake comes from three local private schools. Historically, children in the state system were expected to attend the local Angley School in Cranbrook with the ablest then transferring to Cranbrook at 13, but this has been discouraged recently by Angley, and the entrance test became ratcheted up in terms of required performance. As a result families of local able state school children who don't wish to join the High Weald Academy, replacement for the failed Angley School, are currently forced to look elsewhere to grammar schools in Maidstone, Tonbridge or Tunbridge Wells. This will stop, except for those chasing super selective places, although the cut off distance for successful applicants, currently within the priority catchment area, will inevitably shrink further if the Planned Admission Number of 98 day children is retained (there are also 52 boarding places awarded annually).