We have a school district of 40,000+ and our entire state uses PowerSchool as the SIS. It is able to organize the student data in such a way that we are able to report on our student data as a whole or at individual schools.
As noted, I think it would be hard to find anything else that is better than this tool for your school or district, this SIS is really the total package. It has a great teacher grade book, and while there are always things that can be improved, because you can customize it, the things you cannot live without you do not have to live without.
Any district or school can benefit from it. I am not sure there is a better SIS out there, as I looked into every other one I could find and I think you would be hard pressed to find another. There is always room for improvement, and they would do well to try not to do so many things. Some of these things are broken, and I have to question who is telling them to fix them.