We have all seen the single school example which has a student, course, and teacher table, but what about a database that has more than one school. Obviously, we can't simply insert all the data into a giant student table (etc) because many schools don't assign a student number based upon the ssn (unique number). Is it better then, to create a database for each school, keeping the data separate, or to combine all the students, parents, courses, (etc) into a global database where all the schools can access only their students' data. I can see this as being similar to a giant company that has different departments and employees (as schools is to students). But this would require that I put the unique school ID into many tables such as student, teacher, course, etc.
All responses welcome. I am 50/50 as to which is better.

Thanks