Extra mortgage payments - best method?

I attended a closing a few days ago at an attorney's office (less frequent here in Austin, as we usually close at title companies).  This particular guy has always been very good at explaining the closing process to the buyers and sellers, yet he is also quick.  At any rate, he was telling my buyers that the best method for sending extra payments to the bank/mortgage company was to divide one payment by 12, then send 1/12 each month applied to principal.  He said that this would remove four extra YEARS from the mortgage as opposed to simply sending one extra payment annually all at once.

I know that the other method (one full extra payment sent once a year) will knock off a good portion of the loan term (I think close to half), but I wasn't sure if this other method he recommended would actually whittle it down that much more.  He claimed that it was because of how they amortize loans.  I would be curious to hear comments either way.