is st thomas more middle in NORWICH a private school?

[agasfocus]

what does "voluntary aided" means?!

I don't know about the school you mention but; Voluntary Aided refers to a state (maintained) school which is a Church school. From the parents point of view it makes little difference once the child is in school.
However the Governing body set the admission rules and these are often based around regular church attendance (as well as the usual criteria of siblings, distance, statemented and looked after children etc). The Governing body also have lots of Governors from a Church background and there may be more openly Christian teaching than you are comfortable with.
The Governing body employ the staff, They (the Governing body) also have to pay 10% of all capital building costs, so you may be exposed to a lot of fundraisng.

AFAIK it is the catholic middle school in Norwich.

St Johns is the primary and Notre Dame is the catholic comprehensive.

I think therefore there is probably some admission policy regarding faith.