Does anyone know when you have to commit to a final choice for boys' public schools, particularly Westminster and Eton?

Have a look through the paperwork you have from both schools. Generally you are asked to choose one in the Michaelmas term of year 8 - some people even leave it until around March of year 8 when prep schools enter DC for 1 school for CE. You need to decide if you want to lose your deposit (c£1-2000) I would guess and also read carefully to see when you become liable for the first terms fees (c£11500 for E).

My advice would be to decide earlier as (1) you look like you are choosing between day and boarding - a fairly black and white choice and a very personal choice, (2) they are both great schools with W having the edge academically I would say, given it is more selective, and also having the advantage of girls in the 6th form to provide a more "normal" environment. Also, look at the characteristics of both schools - is your DS competitive - read some of the posts from regular Eton posters - they talk about E being competitive for everything - some DS love this, others will be crushed, especially if not sporty or if they struggle to find their thing there.

What advice is your prep giving you? You will relax more about the whole thing when you have made a decision, and your DS will also appreciate it as he will know where he is heading and what he's aiming for.

The exact dates will be somewhere in the bumf you have.

For many schools, it's some time around March in year 7 for the big deposit.

Schools expect some shuffling at the time the money becomes due. You won't cause any problems for subsequent DC in deciding against taking a conditional place further (as long as you do so within their admin timetable).

I think deposits and commitment are meant to be this term? You could go beyond this date by writing multiple cheques but that would start burning goodwill. Why not start a thread to help you decide - it's a pretty common choice to have to make.

without wishing to sound rude, presumably if he has a conditional offer at these schools, then the paperwork they send give full details of when the entrance deposit has to be paid by and when its too late to change without losing that deposit and/or becoming liable for a whole terms fees in lieu of notice?