In our experience prep heads gets a heads up to help them prepare for results day and, in particular conversations with the parents. That might include children not getting any offer but also, by knowing which offers DC get (or did not get), which advice to provide to parents re: WL, best fit school, etc.
Unsurprisingly, heads are usually very careful not to share that information with parents as it would impact the trust with the senior schools concerned.
Good luck to all waiting for results this week.