As a current, very happy, parent at Sherborne Prep, I can heartily recommend it - my DC are thriving and really love it.
The school recently merged with Sherborne School which is investing financially in its facilities etc.
Lots of very senior staff at the boys’ school also have children at the Prep (there are also very close links with the girls’ school though that is a different legal entity – but many girls move on there).
No sign of any intention to close it!
Numbers did drop during the pandemic but appear to be recovering. Don’t know Clayesmore well, but people I know with children at Leweston are happy with that school too.
For what it’s worth, if this is a concern, the auditors have been recording a going concern material uncertainty for Leweston for some years now, in the accounts on Companies House.
No such note on the Sherborne School accounts (or indeed the Sherborne Prep accounts previously, when it was separate) …
Have a look around all of them and see what works for you!