AD TOOL FOR ADDING AND TAKING OUT users

I am wondering if anyone knows of a third party tool for AD that will allow for better user management in a high school setting.  Every year, we lose about 500 students and gain about 500 students as the old class come in and the new class leaves.  

The problem lies in the fact that the principal can only give me a full list of students (ie not just the ones that are leaving, and the ones that are entering).  I cannot simply delete all the student accounts and re-add them in because a large portion of them have work saved on the server that is tied to their accounts via permission settings.

I am looking for a program that can add in the new students, is able to deal with the accounts that already exist, and take the accounts out of the students that are no longer in the student roster.

currently we are using the CLI AD tools that come with windows 2003.  while i can eventually get the job done, it is painstakingly slow to trudge through the duplicates, and try and figure out who has left.

thank you