How come the Latin they use in church is pronounced completely different from how I learned it in school?

Answer 1

In Latin there are only two distinctions - the literati and the illiterati. There is no possible manner in which one may introduce the vernacular element into an explicatory categorisation.

Answer 2

Schools now teach the nearest approximation it has been possible to reach of the original pronunciation of Latin. Nobody is entirely sure of precisely how the Romans spoke. http://home.scarlet.be/mauk.haemers/collegium_latinum/pronounce.htm
While people tended to speak Latin according to their own native pronunciation, it became fashionable to pronounce Church Latin as if it were Italian. Church Latin owes much to the essentially Italian background of the Roman Catholic Church and to the Italian musical tradition. Here is a link for further reading. http://www.ai.uga.edu/mc/latinpro.pdf

Answer 3

All spoken languages are spoken with an accent. As the only place that Latin is now spoken is in church, it has a "church" accent. That is in addition to the normal accent of the speaker.

The Latin we learnt in school is, as Turk said, how it is thought to have been spoken. BUT, that is of course subject to the speaker's own natural accent. The proper accent would, of course, been at least slightly artificial, much as BBC English is today.

Answer 4

Men of God normally pronounce it with a melodic pronouncation, whilst those who learn it at school just say it as they see it.