The tier questionWhy the Entry Decision Matters So Much
In Maths and the sciences a student sits one of two papers. The easier route is capped at grade 5, so a child aiming higher has to be entered higher, ready or not.
Foundation caps at 5
A Foundation paper cannot award more than a grade 5, whatever the student writes. For a child targeting 6 or above it closes the door before the exam.
Higher starts at 4
Higher runs from 4 up to 9. Entered too early it can produce a lower grade than Foundation would have, because the questions assume more ground is covered.
Schools decide, after mocks
Entries are fixed by the school, normally once mock results are in. That makes the weeks after the mocks the window where the conversation is still useful.