BuddyPress.org

My community is being made to a school, so I want to allow only students this school are able to login.
Each student has his number of registration, and I have this data into a mysql table.
I would like to check, before registration, if this student belongs to my school or not, asking him to enter this number and checking with the database.

Is there an easy way to do this? I understand a little PHP and mysql, but I’m looking for the files and lines for the inclusion in the database and I’m not finding anything.

So I thought I’d do the following, change the button link to register for a temporary page where the student will enter this code if it is correct, then redirect him to complete the registration, otherwise it will not be able to access the register.

Where do I change this URL? or there is another way to do that?

Sorry for my bad english