Gluon, each school has a unique number that you have to bring with you to the test center.
At the end of the test, you will decide to give the go ahead or cancel your score. If you want your scores, then they will be sent to the schools whose numbers you submitted prior to the start of the test.
If you decide to report the score to additional schools, you will have to pay an additional fee. Check http://www.mba.com/mba/TaketheGMAT
What I don't know and I hope someone can answer is, first, what happens if you report the score to a school to which you haven't started the application process? and second, what happens when you submit a score to a school you are applying for in years to come? Anyone?
Oh! gluon.. good luck. Time to collect your 700.