esim for long term travel

Have you checked Giffgaff? That comes recommended here and I believe you can activate in the US. https://help.giffgaff.com/en/collections/626993-esim That said, there are some caveats:

You can use giffgaff in the USA, but you’ll need a pay-as-you-go (PAYG) credit balance on your giffgaff account to do so (goodybags don’t work when you are outside of the UK and EU). Using giffgaff in the USA will cost £1 per minute to make and receive calls, 30p to send a text message and 20p per MB of data used. https://www.uswitch.com/mobiles/guides/giffgaff-international-roaming-faq/

Have you checked with the school? You can't be the first American to have this issue.

+1 for giffgaff- my son was at university in the UK and now works there, and this is what he uses (as do I when I visit). You can get an eSIM, or they can post a physical SIM. Super cheap as well, and allows free roaming in Europe.

" I really want to get this set up soon so I can use the number in applying for other things I need in the UK"

There is a limit to what you can do before you arrive. My main piece of advice is when it comes to banking, use a fintech like Wise - British banks are a bit of a pain to deal with- my son was on the electoral roll before Barclays opened a bank account for him...

Add another recommendation for giffgaff. It's easy to get a giffgaff account while one is still in the USA, their service is fine, and the cost is extremely reasonable. I used one of their accounts for two months this summer and it worked great. They are able to connect to all the major networks in the UK, and also in France.

Efforts in previous summers to secure accounts from EE and O2 were unsuccessful, even after landing in the UK. Vodafone took a great deal of haggling in order to secure a single account for my wife.