A selective system and wide catchments
Kent’s grammar schools draw pupils from considerably wider areas than a typical catchment secondary, and many operate on large sites with substantial grounds. That has a direct effect on lockdown planning.
Wide catchments mean a higher proportion of pupils travelling independently, arriving and leaving across a longer window, and present on site outside the core day. The procedure needs to account for people arriving during an incident, not only those already inside.
Large sites also mean the distance between the furthest occupied point and the nearest trigger can be considerable, which usually argues for portable triggers alongside fixed call points.