I don't know about a week but I know staff find out at least the day the letter is expected and heads maybe a few days before. If there is an issue ie. a child underperforms what the head's reference suggests , there may be a conversation before offers are made.
Really? Even when the schools aren't connected? We are expecting 10+ results this Friday. Will my dd's primary school HT know she is in or not before the letter arrives? She was asked for a reference before the exam was sat. I don't see why she would be informed, we're not a link or feeder prep.
It will depend on the relationship between the senior school and the junior school. Some senior schools will get applicants from over 150 different schools, so will probably only make contact with preps or schools sending over a certain number of pupils.
In my experience our prep head was contacted by the senior schools once the exams were marked, but before interviews, essentially to discuss whether the exam results were a true reflection of ability. Some senior heads have since made contact with the prep and indicated whether places/scholarships will be offered, but for others (where the prep isn't necessarily a significant feeder), I suspect there may be no further contact. Certainly we're always surveyed and asked about offers by the prep, indicating that they're not always given full details by the senior schools.
I think some people are interpreting this question as "do the heads of senior schools know the results of examinations for entrance to their schools before candidates parents do?"; this answer to this is of course yes.
I think the question you are asking is "do the heads of junior schools know the results of examinations for entry of their pupils to (connected or unconnected) senior schools before candidates parents do?"; the answer to this is probably "sometimes yes".
For Common Entrance, the prep school head knows the results two days before they are given to students. This gives them time to negotiate or phone around alternative schools should the worst come to the worst. Students generally tell the parents.
As for an exam that has nothing to do with the prep school, the junior school head will not be informed at all.
For the March 3rd state school offers, primary heads know on the 1st. Very useful for teachers to spot those children who are going to be v. disappointed - we can put pastoral measures in place so they are supported.