When to say to school ( year 3 atm) that the child is leaving at the end of the year

[stripes11]

my DS got a place at a different school ( music specialist boarding school), when si the best time to tell the teacher/ DS' friends that he is going to leave at the end of the year?

Is it a private school? In which case you usually have to give a terms notice otherwise you'll be charged for next terms fees. If it's state you can tell them whenever, however I personally think it's considerate to let them know as soon as possible in case there is a waiting list so they can make other families aware.

Telling the school and telling friends would be different time frames in my opinion.

If it's private then check what notice you need to give school. If it's state then it matters less, but morally I would tell them sooner rather than later so they can offe the place.

I wouldn't tell a state school now. They can't 'offer' the place unless this child is leaving now/has left. When you get offered a state place off a waiting list you pretty much start on the Monday after. You can of course tell them informally and speak to the teacher so they know how to break it gently.

Private schools I have no idea but just make sure you tell them with enough notice.

I would tell the school ASAP, but would hold off telling friends until after Easter. If you are leaving a private school then you will (probably) have to give a term's notice anyway.

Just after half term in the summer term.
No point saying before that, they can't do anything with the info.
(And you never know, you might change your mind re moving.)