That is because you will be offered the highest ranking school that you qualify for. Which is why you need to put them in order of preference.
So the heads are saying if you like our school best then place it first.
https://assets.ctfassets.net/knkzaf64jx ... ochure.pdf Page 11
Quote:
Selective/Grammar schools
You should put your preferred schools on the application form in the order that you want them, and this should include grammar schools if you so wish. You will need to consider the order of schools carefully. School Admissions will offer places according to the highest of your preferences that can be met. Entry to all grammar schools in Essex is based on the results of selection tests. If your child’s selection test score is high enough for him/ her to be offered a grammar school place but you have expressed a higher preference for another school that can be met, your single offer of a place will be at your higher preference school, not the
grammar school.
List the schools in your true order of preference.